diff --git a/docs/options/css.md b/docs/options/css.md
index 3c6890a29..53b765a60 100644
--- a/docs/options/css.md
+++ b/docs/options/css.md
@@ -328,6 +328,94 @@ export function greet() {
 
 This is useful for component libraries where you want CSS to be automatically included when users import your components.
 
+## CSS Modules
+
+Files with the `.module.css` extension (and preprocessor variants like `.module.scss`, `.module.less`, etc.) are treated as [CSS modules](https://github.com/css-modules/css-modules). Class names are automatically scoped and exported as a JavaScript object:
+
+```ts
+// src/index.ts
+import styles from './app.module.css'
+
+console.log(styles.title) // "scoped_title_hash"
+```
+
+```css
+/* app.module.css */
+.title {
+  color: red;
+}
+.content {
+  font-size: 14px;
+}
+```
+
+The CSS is emitted with scoped class names, and the JS output exports the mapping from original to scoped names.
+
+### Configuration
+
+Configure CSS modules behavior via `css.modules`:
+
+```ts
+export default defineConfig({
+  css: {
+    modules: {
+      // Scoping behavior: 'local' (default) or 'global'
+      scopeBehaviour: 'local',
+
+      // Pattern for scoped class names (Lightning CSS pattern syntax)
+      generateScopedName: '[hash]_[local]',
+
+      // Transform class name convention in JS exports
+      localsConvention: 'camelCase',
+    },
+  },
+})
+```
+
+Set `css.modules: false` to disable CSS modules entirely — `.module.css` files will be treated as regular CSS.
+
+### `localsConvention`
+
+Controls how class names are exported in JavaScript:
+
+| Value             | Input     | Exports             |
+| ----------------- | --------- | ------------------- |
+| _(not set)_       | `foo-bar` | `foo-bar`           |
+| `'camelCase'`     | `foo-bar` | `foo-bar`, `fooBar` |
+| `'camelCaseOnly'` | `foo-bar` | `fooBar`            |
+| `'dashes'`        | `foo-bar` | `foo-bar`, `fooBar` |
+| `'dashesOnly'`    | `foo-bar` | `fooBar`            |
+
+### `generateScopedName`
+
+When using `transformer: 'lightningcss'` (default), this accepts a Lightning CSS [pattern string](https://lightningcss.dev/css-modules.html#custom-naming-conventions) (e.g., `'[hash]_[local]'`).
+
+When using `transformer: 'postcss'`, this also accepts a function:
+
+```ts
+export default defineConfig({
+  css: {
+    transformer: 'postcss',
+    modules: {
+      generateScopedName: (name, filename, css) => {
+        return `my-lib_${name}`
+      },
+    },
+  },
+})
+```
+
+> [!NOTE]
+> Function-form `generateScopedName` is only supported with `transformer: 'postcss'`. The Lightning CSS transformer only supports string patterns.
+
+### Optional Dependencies
+
+When using `transformer: 'postcss'` with CSS modules, install [`postcss-modules`](https://github.com/css-modules/postcss-modules):
+
+```bash
+npm install -D postcss postcss-modules
+```
+
 ## CSS Code Splitting
 
 ### Merged Mode (Default)
@@ -372,6 +460,22 @@ dist/
   async-abc123.css ← CSS from async chunk
 ```
 
+## PostCSS Optional Peer Dependencies
+
+When using `transformer: 'postcss'`, the following packages may need to be installed depending on the features you use:
+
+| Package                                                             | Purpose                                  | Required When                          |
+| ------------------------------------------------------------------- | ---------------------------------------- | -------------------------------------- |
+| [`postcss`](https://github.com/postcss/postcss)                     | Core PostCSS engine                      | Always (with `transformer: 'postcss'`) |
+| [`postcss-import`](https://github.com/postcss/postcss-import)       | Resolve and inline `@import` statements  | CSS files use `@import`                |
+| [`postcss-modules`](https://github.com/css-modules/postcss-modules) | CSS modules support (scoped class names) | Using `.module.css` files              |
+
+```bash
+npm install -D postcss postcss-import postcss-modules
+```
+
+All three are declared as optional peer dependencies of `@tsdown/css` and only loaded when needed.
+
 ## Options Reference
 
 | Option                    | Type                          | Default          | Description                                                 |
@@ -380,6 +484,7 @@ dist/
 | `css.splitting`           | `boolean`                     | `false`          | Enable CSS code splitting per chunk                         |
 | `css.fileName`            | `string`                      | `'style.css'`    | File name for the merged CSS file (when `splitting: false`) |
 | `css.minify`              | `boolean`                     | `false`          | Enable CSS minification                                     |
+| `css.modules`             | `object \| false`             | `{}`             | CSS modules configuration, or `false` to disable            |
 | `css.target`              | `string \| string[] \| false` | _from `target`_  | CSS-specific syntax lowering target                         |
 | `css.postcss`             | `string \| object`            | —                | PostCSS config path or inline options                       |
 | `css.preprocessorOptions` | `object`                      | —                | Options for CSS preprocessors                               |
diff --git a/docs/zh-CN/options/css.md b/docs/zh-CN/options/css.md
index 7c23d2e23..1d6f9d84d 100644
--- a/docs/zh-CN/options/css.md
+++ b/docs/zh-CN/options/css.md
@@ -328,6 +328,94 @@ export function greet() {
 
 这对于组件库非常有用，可以确保用户导入组件时自动包含对应的 CSS。
 
+## CSS Modules
+
+扩展名为 `.module.css` 的文件（以及预处理器变体如 `.module.scss`、`.module.less` 等）会被视为 [CSS Modules](https://github.com/css-modules/css-modules)。类名会自动添加作用域，并作为 JavaScript 对象导出：
+
+```ts
+// src/index.ts
+import styles from './app.module.css'
+
+console.log(styles.title) // "scoped_title_hash"
+```
+
+```css
+/* app.module.css */
+.title {
+  color: red;
+}
+.content {
+  font-size: 14px;
+}
+```
+
+CSS 会以作用域化的类名输出，JS 输出导出原始类名到作用域化类名的映射。
+
+### 配置
+
+通过 `css.modules` 配置 CSS modules 行为：
+
+```ts
+export default defineConfig({
+  css: {
+    modules: {
+      // 作用域行为：'local'（默认）或 'global'
+      scopeBehaviour: 'local',
+
+      // 作用域类名模式（Lightning CSS 模式语法）
+      generateScopedName: '[hash]_[local]',
+
+      // JS 导出中的类名转换约定
+      localsConvention: 'camelCase',
+    },
+  },
+})
+```
+
+设置 `css.modules: false` 可完全禁用 CSS modules——`.module.css` 文件将被视为普通 CSS。
+
+### `localsConvention`
+
+控制类名在 JavaScript 中的导出方式：
+
+| 值                | 输入      | 导出                |
+| ----------------- | --------- | ------------------- |
+| _（未设置）_      | `foo-bar` | `foo-bar`           |
+| `'camelCase'`     | `foo-bar` | `foo-bar`、`fooBar` |
+| `'camelCaseOnly'` | `foo-bar` | `fooBar`            |
+| `'dashes'`        | `foo-bar` | `foo-bar`、`fooBar` |
+| `'dashesOnly'`    | `foo-bar` | `fooBar`            |
+
+### `generateScopedName`
+
+使用 `transformer: 'lightningcss'`（默认）时，接受 Lightning CSS [模式字符串](https://lightningcss.dev/css-modules.html#custom-naming-conventions)（如 `'[hash]_[local]'`）。
+
+使用 `transformer: 'postcss'` 时，还支持函数形式：
+
+```ts
+export default defineConfig({
+  css: {
+    transformer: 'postcss',
+    modules: {
+      generateScopedName: (name, filename, css) => {
+        return `my-lib_${name}`
+      },
+    },
+  },
+})
+```
+
+> [!NOTE]
+> 函数形式的 `generateScopedName` 仅在 `transformer: 'postcss'` 时支持。Lightning CSS 转换器仅支持字符串模式。
+
+### 可选依赖
+
+使用 `transformer: 'postcss'` 配合 CSS modules 时，需安装 [`postcss-modules`](https://github.com/css-modules/postcss-modules)：
+
+```bash
+npm install -D postcss postcss-modules
+```
+
 ## CSS 代码分割
 
 ### 合并模式（默认）
@@ -372,6 +460,22 @@ dist/
   async-abc123.css ← 异步 chunk 的 CSS
 ```
 
+## PostCSS 可选依赖
+
+使用 `transformer: 'postcss'` 时，根据使用的功能可能需要安装以下包：
+
+| 包                                                                  | 用途                           | 何时需要                                     |
+| ------------------------------------------------------------------- | ------------------------------ | -------------------------------------------- |
+| [`postcss`](https://github.com/postcss/postcss)                     | PostCSS 核心引擎               | 始终需要（使用 `transformer: 'postcss'` 时） |
+| [`postcss-import`](https://github.com/postcss/postcss-import)       | 解析和内联 `@import` 语句      | CSS 文件使用 `@import` 时                    |
+| [`postcss-modules`](https://github.com/css-modules/postcss-modules) | CSS modules 支持（作用域类名） | 使用 `.module.css` 文件时                    |
+
+```bash
+npm install -D postcss postcss-import postcss-modules
+```
+
+这三个包都声明为 `@tsdown/css` 的可选 peer dependencies，仅在需要时加载。
+
 ## 选项参考
 
 | 选项                      | 类型                          | 默认值           | 描述                                          |
@@ -380,6 +484,7 @@ dist/
 | `css.splitting`           | `boolean`                     | `false`          | 启用按 chunk 的 CSS 代码分割                  |
 | `css.fileName`            | `string`                      | `'style.css'`    | 合并 CSS 的文件名（当 `splitting: false` 时） |
 | `css.minify`              | `boolean`                     | `false`          | 启用 CSS 压缩                                 |
+| `css.modules`             | `object \| false`             | `{}`             | CSS modules 配置，或 `false` 禁用             |
 | `css.target`              | `string \| string[] \| false` | _继承 `target`_  | CSS 专用语法降级目标                          |
 | `css.postcss`             | `string \| object`            | —                | PostCSS 配置路径或内联选项                    |
 | `css.preprocessorOptions` | `object`                      | —                | CSS 预处理器选项                              |
diff --git a/packages/css/package.json b/packages/css/package.json
index 7ed85811d..54391f282 100644
--- a/packages/css/package.json
+++ b/packages/css/package.json
@@ -50,6 +50,7 @@
   "peerDependencies": {
     "postcss": "^8.4.0",
     "postcss-import": "^16.0.0",
+    "postcss-modules": "^6.0.0",
     "sass": "*",
     "sass-embedded": "*",
     "tsdown": "workspace:*"
@@ -61,6 +62,9 @@
     "postcss-import": {
       "optional": true
     },
+    "postcss-modules": {
+      "optional": true
+    },
     "sass": {
       "optional": true
     },
diff --git a/packages/css/src/index.ts b/packages/css/src/index.ts
index 73db5a107..5417c970e 100644
--- a/packages/css/src/index.ts
+++ b/packages/css/src/index.ts
@@ -1,6 +1,7 @@
 export { resolveCssOptions } from './options.ts'
 export { CssPlugin } from './plugin.ts'
 export type {
+  CSSModulesOptions,
   CssOptions,
   LessPreprocessorOptions,
   LightningCSSOptions,
diff --git a/packages/css/src/lightningcss.ts b/packages/css/src/lightningcss.ts
index 1f6426b84..d223ec5a5 100644
--- a/packages/css/src/lightningcss.ts
+++ b/packages/css/src/lightningcss.ts
@@ -1,9 +1,10 @@
 import { readFileSync } from 'node:fs'
 import path from 'node:path'
+import { extractLightningCssModuleExports } from './modules.ts'
 import { compilePreprocessor, getPreprocessorLang } from './preprocessors.ts'
 import { getCssResolver, resolveWithResolver } from './resolve.ts'
 import type { LightningCSSOptions, PreprocessorOptions } from './options.ts'
-import type { Targets } from 'lightningcss'
+import type { CSSModulesConfig, Targets } from 'lightningcss'
 import type { Logger } from 'tsdown/internal'
 
 const encoder = new TextEncoder()
@@ -13,12 +14,19 @@ export interface TransformCssOptions {
   target?: string[]
   lightningcss?: LightningCSSOptions
   minify?: boolean
+  cssModules?: boolean | CSSModulesConfig
+}
+
+export interface TransformCssResult {
+  code: string
+  modules?: Record<string, string>
 }
 
 export interface BundleCssOptions {
   target?: string[]
   lightningcss?: LightningCSSOptions
   minify?: boolean
+  cssModules?: boolean | CSSModulesConfig
   preprocessorOptions?: PreprocessorOptions
   logger: Logger
 }
@@ -26,18 +34,24 @@ export interface BundleCssOptions {
 export interface BundleCssResult {
   code: string
   deps: string[]
+  modules?: Record<string, string>
 }
 
 export async function transformWithLightningCSS(
   code: string,
   filename: string,
   options: TransformCssOptions,
-): Promise<string> {
+): Promise<TransformCssResult> {
   const targets =
     options.lightningcss?.targets ??
     (options.target ? esbuildTargetToLightningCSS(options.target) : undefined)
-  if (!targets && !options.lightningcss && !options.minify) {
-    return code
+  if (
+    !targets &&
+    !options.lightningcss &&
+    !options.minify &&
+    !options.cssModules
+  ) {
+    return { code }
   }
 
   const { transform } = await import('lightningcss')
@@ -47,9 +61,15 @@ export async function transformWithLightningCSS(
     ...options.lightningcss,
     targets,
     minify: options.minify,
+    cssModules: options.cssModules,
   })
 
-  return decoder.decode(result.code)
+  return {
+    code: decoder.decode(result.code),
+    modules: result.exports
+      ? extractLightningCssModuleExports(result.exports)
+      : undefined,
+  }
 }
 
 export async function bundleWithLightningCSS(
@@ -69,6 +89,7 @@ export async function bundleWithLightningCSS(
     ...options.lightningcss,
     targets,
     minify: options.minify,
+    cssModules: options.cssModules,
     resolver: {
       async read(filePath: string) {
         let fileCode: string
@@ -108,6 +129,9 @@ export async function bundleWithLightningCSS(
   return {
     code: new TextDecoder().decode(result.code),
     deps,
+    modules: result.exports
+      ? extractLightningCssModuleExports(result.exports)
+      : undefined,
   }
 }
 
diff --git a/packages/css/src/modules.ts b/packages/css/src/modules.ts
new file mode 100644
index 000000000..48a9283f7
--- /dev/null
+++ b/packages/css/src/modules.ts
@@ -0,0 +1,70 @@
+import type { CSSModuleExports } from 'lightningcss'
+
+const VALID_ID_RE = /^[$_a-z][$\w]*$/i
+
+export function modulesToEsm(modules: Record<string, string>): string {
+  const lines: string[] = []
+  for (const [key, value] of Object.entries(modules)) {
+    if (VALID_ID_RE.test(key)) {
+      lines.push(`export const ${key} = ${JSON.stringify(value)};`)
+    }
+  }
+  lines.push(`export default ${JSON.stringify(modules)};`)
+  return lines.join('\n')
+}
+
+function dashToCamel(str: string): string {
+  return str.replaceAll(/-([a-z])/g, (_, c: string) => c.toUpperCase())
+}
+
+export function applyLocalsConvention(
+  modules: Record<string, string>,
+  convention: 'camelCase' | 'camelCaseOnly' | 'dashes' | 'dashesOnly',
+): Record<string, string> {
+  const result: Record<string, string> = {}
+  for (const [key, value] of Object.entries(modules)) {
+    const camelized = dashToCamel(key)
+    switch (convention) {
+      case 'camelCase':
+        result[key] = value
+        if (camelized !== key) {
+          result[camelized] = value
+        }
+        break
+      case 'camelCaseOnly':
+        result[camelized] = value
+        break
+      case 'dashes':
+        result[key] = value
+        if (key.includes('-')) {
+          result[camelized] = value
+        }
+        break
+      case 'dashesOnly':
+        if (key.includes('-')) {
+          result[camelized] = value
+        } else {
+          result[key] = value
+        }
+        break
+    }
+  }
+  return result
+}
+
+export function extractLightningCssModuleExports(
+  exports: CSSModuleExports,
+): Record<string, string> {
+  const modules: Record<string, string> = {}
+  const sortedEntries = Object.entries(exports).toSorted(([a], [b]) =>
+    a.localeCompare(b),
+  )
+  for (const [key, value] of sortedEntries) {
+    let name = value.name
+    for (const c of value.composes) {
+      name += ` ${c.name}`
+    }
+    modules[key] = name
+  }
+  return modules
+}
diff --git a/packages/css/src/options.test.ts b/packages/css/src/options.test.ts
index 761a96358..765b88e57 100644
--- a/packages/css/src/options.test.ts
+++ b/packages/css/src/options.test.ts
@@ -10,6 +10,7 @@ describe('resolveCssOptions', () => {
       fileName: defaultCssBundleName,
       minify: false,
       inject: false,
+      modules: {},
       target: undefined,
       preprocessorOptions: undefined,
       lightningcss: undefined,
@@ -42,6 +43,26 @@ describe('resolveCssOptions', () => {
     expect(result.target).toBeUndefined()
   })
 
+  test('modules defaults to empty object', () => {
+    const result = resolveCssOptions()
+    expect(result.modules).toEqual({})
+  })
+
+  test('modules=false disables CSS modules', () => {
+    const result = resolveCssOptions({ modules: false })
+    expect(result.modules).toBe(false)
+  })
+
+  test('modules config is passed through', () => {
+    const result = resolveCssOptions({
+      modules: { localsConvention: 'camelCase', hashPrefix: 'app' },
+    })
+    expect(result.modules).toEqual({
+      localsConvention: 'camelCase',
+      hashPrefix: 'app',
+    })
+  })
+
   test('custom options are passed through', () => {
     const result = resolveCssOptions({
       transformer: 'postcss',
@@ -59,6 +80,7 @@ describe('resolveCssOptions', () => {
       fileName: 'custom.css',
       minify: true,
       inject: true,
+      modules: {},
       target: undefined,
       preprocessorOptions: { scss: { additionalData: '$x: 1;' } },
       lightningcss: { drafts: { customMedia: true } },
diff --git a/packages/css/src/options.ts b/packages/css/src/options.ts
index 4388d0319..99a02f34d 100644
--- a/packages/css/src/options.ts
+++ b/packages/css/src/options.ts
@@ -11,6 +11,51 @@ export type LightningCSSOptions = Omit<
   'filename' | 'code'
 >
 
+export interface CSSModulesOptions {
+  /**
+   * Controls the scoping behavior.
+   * @default 'local'
+   */
+  scopeBehaviour?: 'global' | 'local'
+
+  /**
+   * File paths matching these patterns will use global scoping.
+   */
+  globalModulePaths?: RegExp[]
+
+  /**
+   * Pattern or function to generate scoped class names.
+   * When using `transformer: 'lightningcss'`, only string patterns are supported.
+   */
+  generateScopedName?:
+    | string
+    | ((name: string, filename: string, css: string) => string)
+
+  /**
+   * Prefix added to hashes when generating scoped names.
+   */
+  hashPrefix?: string
+
+  /**
+   * Transform convention for exported class names.
+   */
+  localsConvention?: 'camelCase' | 'camelCaseOnly' | 'dashes' | 'dashesOnly'
+
+  /**
+   * Whether to include global class names in the export.
+   */
+  exportGlobals?: boolean
+
+  /**
+   * Callback to receive the generated class name mappings.
+   */
+  getJSON?: (
+    cssFileName: string,
+    json: Record<string, string>,
+    outputFileName: string,
+  ) => void
+}
+
 export interface CssOptions {
   /**
    * Enable/disable CSS code splitting.
@@ -77,6 +122,15 @@ export interface CssOptions {
    */
   inject?: boolean
 
+  /**
+   * CSS modules configuration.
+   * When not `false`, `.module.css` files (and preprocessor variants) are
+   * treated as CSS modules with scoped class names.
+   *
+   * @see https://github.com/css-modules/css-modules
+   */
+  modules?: CSSModulesOptions | false
+
   /**
    * CSS transformer to use. Controls how CSS is processed:
    *
@@ -140,7 +194,7 @@ export interface StylusPreprocessorOptions {
 export type ResolvedCssOptions = Overwrite<
   MarkPartial<
     Required<CssOptions>,
-    'preprocessorOptions' | 'lightningcss' | 'postcss'
+    'preprocessorOptions' | 'lightningcss' | 'postcss' | 'modules'
   >,
   { target?: string[] }
 >
@@ -166,6 +220,7 @@ export function resolveCssOptions(
     fileName: options.fileName ?? defaultCssBundleName,
     minify: options.minify ?? false,
     inject: options.inject ?? false,
+    modules: options.modules === false ? false : (options.modules ?? {}),
     target: cssTarget,
     preprocessorOptions: options.preprocessorOptions,
     lightningcss: options.lightningcss,
diff --git a/packages/css/src/plugin.ts b/packages/css/src/plugin.ts
index f5a6823e7..7cf316bb6 100644
--- a/packages/css/src/plugin.ts
+++ b/packages/css/src/plugin.ts
@@ -4,17 +4,24 @@ import {
   bundleWithLightningCSS,
   transformWithLightningCSS,
 } from './lightningcss.ts'
-import { resolveCssOptions, type ResolvedCssOptions } from './options.ts'
+import { applyLocalsConvention, modulesToEsm } from './modules.ts'
+import {
+  resolveCssOptions,
+  type CSSModulesOptions,
+  type ResolvedCssOptions,
+} from './options.ts'
 import { CssPostPlugin, type CssStyles } from './post.ts'
 import { processWithPostCSS as runPostCSS } from './postcss.ts'
 import { compilePreprocessor, getPreprocessorLang } from './preprocessors.ts'
 import {
   CSS_LANGS_RE,
+  CSS_MODULE_RE,
   getCleanId,
   RE_CSS,
   RE_CSS_INLINE,
   RE_INLINE,
 } from './utils.ts'
+import type { CSSModulesConfig } from 'lightningcss'
 import type { Plugin } from 'rolldown'
 import type { ResolvedConfig } from 'tsdown'
 import type { Logger } from 'tsdown/internal'
@@ -87,19 +94,37 @@ export function CssPlugin(
         // where the clean path itself is not a CSS file.
         if (id !== cleanId && !isInline && CSS_LANGS_RE.test(cleanId)) return
 
+        const isModule =
+          !isInline &&
+          cssConfig.css.modules !== false &&
+          CSS_MODULE_RE.test(cleanId)
+
         const deps: string[] = []
+        let modules: Record<string, string> | undefined
 
         if (cssConfig.css.transformer === 'lightningcss') {
-          code = await processWithLightningCSS(
+          const result = await processWithLightningCSS(
             code,
             id,
             cleanId,
             deps,
             cssConfig,
             logger,
+            isModule,
           )
+          code = result.code
+          modules = result.modules
         } else {
-          code = await processWithPostCSS(code, id, cleanId, deps, cssConfig)
+          const result = await processWithPostCSS(
+            code,
+            id,
+            cleanId,
+            deps,
+            cssConfig,
+            isModule,
+          )
+          code = result.code
+          modules = result.modules
         }
 
         for (const dep of deps) {
@@ -110,6 +135,20 @@ export function CssPlugin(
           code += '\n'
         }
 
+        if (modules) {
+          const modulesConfig =
+            typeof cssConfig.css.modules === 'object'
+              ? cssConfig.css.modules
+              : undefined
+          if (modulesConfig?.localsConvention) {
+            modules = applyLocalsConvention(
+              modules,
+              modulesConfig.localsConvention,
+            )
+          }
+          modulesConfig?.getJSON?.(cleanId, modules, cleanId)
+        }
+
         if (isInline) {
           return {
             code: `export default ${JSON.stringify(code)};`,
@@ -118,7 +157,18 @@ export function CssPlugin(
           }
         }
 
-        styles.set(id, code)
+        if (code.length) {
+          styles.set(id, code)
+        }
+
+        if (modules) {
+          return {
+            code: modulesToEsm(modules),
+            moduleSideEffects: false,
+            moduleType: 'js',
+          }
+        }
+
         return {
           code: '',
           moduleSideEffects: 'no-treeshake',
@@ -226,6 +276,36 @@ export function CssPlugin(
   return plugins
 }
 
+interface ProcessResult {
+  code: string
+  modules?: Record<string, string>
+}
+
+function resolveCssModulesConfig(
+  modulesOptions: CSSModulesOptions | false | undefined,
+  isModule: boolean,
+  logger: Logger,
+): boolean | CSSModulesConfig | undefined {
+  if (!isModule) return undefined
+
+  const config = typeof modulesOptions === 'object' ? modulesOptions : undefined
+  if (!config) return true
+
+  const cssModulesConfig: CSSModulesConfig = {}
+  if (typeof config.generateScopedName === 'string') {
+    cssModulesConfig.pattern = config.generateScopedName
+  } else if (typeof config.generateScopedName === 'function') {
+    logger.warn(
+      '[@tsdown/css] `generateScopedName` as a function is not supported with `transformer: "lightningcss"`. Use a string pattern or switch to `transformer: "postcss"`.',
+    )
+  }
+  if (config.scopeBehaviour === 'global') {
+    cssModulesConfig.pattern = '[local]'
+  }
+
+  return Object.keys(cssModulesConfig).length > 0 ? cssModulesConfig : true
+}
+
 async function processWithLightningCSS(
   code: string,
   id: string,
@@ -233,8 +313,14 @@ async function processWithLightningCSS(
   deps: string[],
   config: CssPluginConfig,
   logger: Logger,
-): Promise<string> {
+  isModule: boolean,
+): Promise<ProcessResult> {
   const lang = getPreprocessorLang(cleanId)
+  const cssModules = resolveCssModulesConfig(
+    config.css.modules,
+    isModule,
+    logger,
+  )
 
   if (lang) {
     const preResult = await compilePreprocessor(
@@ -249,6 +335,7 @@ async function processWithLightningCSS(
       target: config.css.target,
       lightningcss: config.css.lightningcss,
       minify: config.css.minify,
+      cssModules,
     })
   }
 
@@ -259,6 +346,7 @@ async function processWithLightningCSS(
       target: config.css.target,
       lightningcss: config.css.lightningcss,
       minify: config.css.minify,
+      cssModules,
     })
   }
 
@@ -269,16 +357,17 @@ async function processWithLightningCSS(
         target: config.css.target,
         lightningcss: config.css.lightningcss,
         minify: config.css.minify,
+        cssModules,
         preprocessorOptions: config.css.preprocessorOptions,
         logger,
       },
       code,
     )
     deps.push(...bundleResult.deps)
-    return bundleResult.code
+    return { code: bundleResult.code, modules: bundleResult.modules }
   }
 
-  return ''
+  return { code: '' }
 }
 
 async function processWithPostCSS(
@@ -287,7 +376,8 @@ async function processWithPostCSS(
   cleanId: string,
   deps: string[],
   config: CssPluginConfig,
-): Promise<string> {
+  isModule: boolean,
+): Promise<ProcessResult> {
   const lang = getPreprocessorLang(cleanId)
 
   if (lang) {
@@ -301,6 +391,9 @@ async function processWithPostCSS(
     deps.push(...preResult.deps)
   }
 
+  const modulesConfig =
+    typeof config.css.modules === 'object' ? config.css.modules : undefined
+
   const needInlineImport = code.includes('@import')
   const postcssResult = await runPostCSS(
     code,
@@ -308,15 +401,18 @@ async function processWithPostCSS(
     config.css.postcss,
     config.cwd,
     needInlineImport,
+    isModule ? { isModule: true, config: modulesConfig } : undefined,
   )
   code = postcssResult.code
   deps.push(...postcssResult.deps)
 
-  return transformWithLightningCSS(code, cleanId, {
+  const transformResult = await transformWithLightningCSS(code, cleanId, {
     target: config.css.target,
     lightningcss: config.css.lightningcss,
     minify: config.css.minify,
   })
+
+  return { code: transformResult.code, modules: postcssResult.modules }
 }
 
 function isEmptyChunkCode(code: string): boolean {
diff --git a/packages/css/src/postcss.ts b/packages/css/src/postcss.ts
index 7c138d01b..c01824db5 100644
--- a/packages/css/src/postcss.ts
+++ b/packages/css/src/postcss.ts
@@ -1,5 +1,5 @@
 import { importWithError } from 'tsdown/internal'
-import type { PostCSSOptions } from './options.ts'
+import type { CSSModulesOptions, PostCSSOptions } from './options.ts'
 
 interface PostCSSConfigResult {
   options: Record<string, any>
@@ -9,6 +9,12 @@ interface PostCSSConfigResult {
 interface PostCSSProcessResult {
   code: string
   deps: string[]
+  modules?: Record<string, string>
+}
+
+export interface PostCSSModulesOptions {
+  isModule: boolean
+  config?: CSSModulesOptions
 }
 
 const fileConfigCache = new Map<
@@ -63,11 +69,36 @@ export async function processWithPostCSS(
   postcssOption: PostCSSOptions | undefined,
   cwd: string,
   injectImport?: boolean,
+  modulesOptions?: PostCSSModulesOptions,
 ): Promise<PostCSSProcessResult> {
   const config = await resolvePostCSSConfig(postcssOption, cwd)
 
   const plugins: any[] = []
 
+  let modules: Record<string, string> | undefined
+
+  if (modulesOptions?.isModule) {
+    const postcssModules: any = await importWithError('postcss-modules')
+    const {
+      localsConvention: _,
+      getJSON: userGetJSON,
+      ...rest
+    } = modulesOptions.config ?? {}
+    plugins.push(
+      (postcssModules.default ?? postcssModules)({
+        ...rest,
+        getJSON(
+          cssFileName: string,
+          json: Record<string, string>,
+          outputFileName: string,
+        ) {
+          modules = json
+          userGetJSON?.(cssFileName, json, outputFileName)
+        },
+      }),
+    )
+  }
+
   if (injectImport) {
     const postcssImport: any = await importWithError('postcss-import')
     plugins.push((postcssImport.default ?? postcssImport)())
@@ -100,5 +131,5 @@ export async function processWithPostCSS(
     }
   }
 
-  return { code: result.css, deps }
+  return { code: result.css, deps, modules }
 }
diff --git a/packages/css/src/utils.ts b/packages/css/src/utils.ts
index ffe874441..85cbdbf07 100644
--- a/packages/css/src/utils.ts
+++ b/packages/css/src/utils.ts
@@ -5,6 +5,9 @@ export const CSS_LANGS_RE: RegExp =
 export const RE_CSS_INLINE: RegExp =
   /\.(?:css|less|sass|scss|styl|stylus)\?(?:.*&)?inline\b/
 
+export const CSS_MODULE_RE: RegExp =
+  /\.module\.(?:css|less|sass|scss|styl|stylus)(?:$|\?)/
+
 export function getCleanId(id: string): string {
   const queryIndex = id.indexOf('?')
   return queryIndex === -1 ? id : id.slice(0, queryIndex)
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 691bd9112..90747f2f8 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -384,10 +384,10 @@ importers:
         version: 0.5.7
       unplugin-vue:
         specifier: catalog:dev
-        version: 7.1.1(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(vue@3.5.30(typescript@5.9.3))(yaml@2.8.2)
+        version: 7.1.1(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(vue@3.5.30(typescript@5.9.3))(yaml@2.8.2)
       vite:
         specifier: ^8.0.0
-        version: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
+        version: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
       vitest:
         specifier: catalog:dev
         version: 4.1.0(@types/node@25.5.0)(@vitest/ui@4.1.0)(vite@8.0.0)
@@ -424,13 +424,13 @@ importers:
         version: 1.1.2(typedoc-plugin-markdown@4.10.0(typedoc@0.28.17(typescript@5.9.3)))
       vite:
         specifier: ^8.0.0
-        version: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
+        version: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
       vitepress:
         specifier: catalog:docs
         version: 2.0.0-alpha.16(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(change-case@5.4.4)(jiti@2.6.1)(oxc-minify@0.119.0)(postcss@8.5.8)(sass-embedded@1.98.0)(sass@1.98.0)(typescript@5.9.3)(yaml@2.8.2)
       vitepress-plugin-group-icons:
         specifier: catalog:docs
-        version: 1.7.1(vite@8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2))
+        version: 1.7.1(vite@8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2))
       vitepress-plugin-llms:
         specifier: catalog:docs
         version: 1.11.0
@@ -467,6 +467,9 @@ importers:
       postcss-load-config:
         specifier: catalog:prod
         version: 6.0.1(jiti@2.6.1)(postcss@8.5.8)(yaml@2.8.2)
+      postcss-modules:
+        specifier: ^6.0.0
+        version: 6.0.1(postcss@8.5.8)
       rolldown:
         specifier: 1.0.0-rc.9
         version: 1.0.0-rc.9
@@ -2768,6 +2771,9 @@ packages:
   fzf@0.5.2:
     resolution: {integrity: sha512-Tt4kuxLXFKHy8KT40zwsUPUkg1CrsgY25FxA2U/j/0WgEDCk3ddc/zLTCCcbSHX9FcKtLuVaDGtGE/STWC+j3Q==}
 
+  generic-names@4.0.0:
+    resolution: {integrity: sha512-ySFolZQfw9FoDb3ed9d80Cm9f0+r7qj+HJkWjeD9RBfpxEVTlVhol+gvaQB/78WbwYfbnNh8nWHHBSlg072y6A==}
+
   get-caller-file@2.0.5:
     resolution: {integrity: sha512-DyFP3BM/3YHTQOCUL/w0OZHR0lpKeGrxotcHWcqNEdnltqFwXVfhEBQ94eIo34AfQpo0rGki4cyIiftY06h2Fg==}
     engines: {node: 6.* || 8.* || >= 10.*}
@@ -2857,6 +2863,12 @@ packages:
     resolution: {integrity: sha512-Y93lCzHYgGWdrJ66yIktxiaGULYc6oGiABxhcO5AufBeOyoIdZF7bIfLaOrbM0iGIOXQQgxxRrFEnb+Y6w1n4A==}
     engines: {node: '>=10.18'}
 
+  icss-utils@5.1.0:
+    resolution: {integrity: sha512-soFhflCVWLfRNOPU3iv5Z9VUdT44xFRbzjLsEzSr5AQmgqPMTHdU3PMT1Cf1ssx8fLNJDA1juftYl+PUcv3MqA==}
+    engines: {node: ^10 || ^12 || >= 14}
+    peerDependencies:
+      postcss: ^8.1.0
+
   ignore@5.3.2:
     resolution: {integrity: sha512-hsBTNUqQTDwkWtcdYI2i06Y/nUBEsNEDJKjWdigLvegy8kDuJAS8uRlpkkcQpyEXL0Z/pjDy5HBmMjRCJ2gq+g==}
     engines: {node: '>= 4'}
@@ -3114,10 +3126,17 @@ packages:
   linkify-it@5.0.0:
     resolution: {integrity: sha512-5aHCbzQRADcdP+ATqnDuhhJ/MRIqDkZX5pyjFHRRysS8vZ5AbqGEoFIb6pYHPZ+L/OC2Lc+xT8uHVVR5CAK/wQ==}
 
+  loader-utils@3.3.1:
+    resolution: {integrity: sha512-FMJTLMXfCLMLfJxcX9PFqX5qD88Z5MRGaZCVzfuqeZSPsyiBzs+pahDQjbIWz2QIzPZz0NX9Zy4FX3lmK6YHIg==}
+    engines: {node: '>= 12.13.0'}
+
   locate-path@6.0.0:
     resolution: {integrity: sha512-iPZK6eYjbxRu3uB4/WZ3EsEIMJFMqAoopl3R+zuq0UjcAm/MO6KCweDgPfP3elTztoKP3KtnVHxTn2NHBSDVUw==}
     engines: {node: '>=10'}
 
+  lodash.camelcase@4.3.0:
+    resolution: {integrity: sha512-TwuEnCnxbc3rAvhf/LbG7tJUDzhqXyFnv3dtzLOPgCG/hODL7WFnsbwktkD7yUV0RrreP/l1PALq/YSg6VvjlA==}
+
   lodash.merge@4.6.2:
     resolution: {integrity: sha512-0KpjqXRVvrYyCsX1swR/XTK0va6VQkQM6MNo7PqW77ByjAhoARA8EfrP1N4+KlKj8YS0ZUCtRT/YUuhyYDujIQ==}
 
@@ -3512,6 +3531,35 @@ packages:
       yaml:
         optional: true
 
+  postcss-modules-extract-imports@3.1.0:
+    resolution: {integrity: sha512-k3kNe0aNFQDAZGbin48pL2VNidTF0w4/eASDsxlyspobzU3wZQLOGj7L9gfRe0Jo9/4uud09DsjFNH7winGv8Q==}
+    engines: {node: ^10 || ^12 || >= 14}
+    peerDependencies:
+      postcss: ^8.1.0
+
+  postcss-modules-local-by-default@4.2.0:
+    resolution: {integrity: sha512-5kcJm/zk+GJDSfw+V/42fJ5fhjL5YbFDl8nVdXkJPLLW+Vf9mTD5Xe0wqIaDnLuL2U6cDNpTr+UQ+v2HWIBhzw==}
+    engines: {node: ^10 || ^12 || >= 14}
+    peerDependencies:
+      postcss: ^8.1.0
+
+  postcss-modules-scope@3.2.1:
+    resolution: {integrity: sha512-m9jZstCVaqGjTAuny8MdgE88scJnCiQSlSrOWcTQgM2t32UBe+MUmFSO5t7VMSfAf/FJKImAxBav8ooCHJXCJA==}
+    engines: {node: ^10 || ^12 || >= 14}
+    peerDependencies:
+      postcss: ^8.1.0
+
+  postcss-modules-values@4.0.0:
+    resolution: {integrity: sha512-RDxHkAiEGI78gS2ofyvCsu7iycRv7oqw5xMWn9iMoR0N/7mf9D50ecQqUo5BZ9Zh2vH4bCUR/ktCqbB9m8vJjQ==}
+    engines: {node: ^10 || ^12 || >= 14}
+    peerDependencies:
+      postcss: ^8.1.0
+
+  postcss-modules@6.0.1:
+    resolution: {integrity: sha512-zyo2sAkVvuZFFy0gc2+4O+xar5dYlaVy/ebO24KT0ftk/iJevSNyPyQellsBLlnccwh7f6V6Y4GvuKRYToNgpQ==}
+    peerDependencies:
+      postcss: ^8.0.0
+
   postcss-selector-parser@7.1.1:
     resolution: {integrity: sha512-orRsuYpJVw8LdAwqqLykBj9ecS5/cRHlI5+nvTo8LcCKmzDmqVORXtOIYEEQuL9D4BxtA1lm5isAqzQZCoQ6Eg==}
     engines: {node: '>=4'}
@@ -3878,6 +3926,9 @@ packages:
   std-env@4.0.0:
     resolution: {integrity: sha512-zUMPtQ/HBY3/50VbpkupYHbRroTRZJPRLvreamgErJVys0ceuzMkD44J/QjqhHjOzK42GQ3QZIeFG1OYfOtKqQ==}
 
+  string-hash@1.1.3:
+    resolution: {integrity: sha512-kJUvRUFK49aub+a7T1nNE66EJbZBMnBgoC1UbCZ5n6bsZKBRga4KgBRTMn/pFkeCZSYtNeSyMxPDM0AXWELk2A==}
+
   string-width@4.2.3:
     resolution: {integrity: sha512-wKyQRQpjJ0sIp62ErSZdGsjMJWsap5oRNihHhu6G7JVO/9jIB6UyevL+tXuOqrng8j/cxKTWyWUwvSTriiZz/g==}
     engines: {node: '>=8'}
@@ -5788,14 +5839,14 @@ snapshots:
       pathe: 2.0.3
       tinyglobby: 0.2.15
       unplugin-utils: 0.3.1
-      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
+      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
 
   '@vitejs/devtools-kit@0.1.0(typescript@5.9.3)(vite@8.0.0)(ws@8.19.0)':
     dependencies:
       '@vitejs/devtools-rpc': 0.1.0(typescript@5.9.3)(ws@8.19.0)
       birpc: 4.0.0
       immer: 11.1.4
-      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
+      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
     transitivePeerDependencies:
       - typescript
       - ws
@@ -5884,7 +5935,7 @@ snapshots:
       perfect-debounce: 2.1.0
       sirv: 3.0.2
       tinyexec: 1.0.4
-      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
+      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
       ws: 8.19.0
     transitivePeerDependencies:
       - '@azure/app-configuration'
@@ -5912,10 +5963,10 @@ snapshots:
       - utf-8-validate
       - vue
 
-  '@vitejs/plugin-vue@6.0.5(vite@8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2))(vue@3.5.30(typescript@5.9.3))':
+  '@vitejs/plugin-vue@6.0.5(vite@8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2))(vue@3.5.30(typescript@5.9.3))':
     dependencies:
       '@rolldown/pluginutils': 1.0.0-rc.2
-      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
+      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
       vue: 3.5.30(typescript@5.9.3)
 
   '@vitest/coverage-v8@4.1.0(vitest@4.1.0)':
@@ -5947,7 +5998,7 @@ snapshots:
       estree-walker: 3.0.3
       magic-string: 0.30.21
     optionalDependencies:
-      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
+      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
 
   '@vitest/pretty-format@4.1.0':
     dependencies:
@@ -6724,6 +6775,10 @@ snapshots:
 
   fzf@0.5.2: {}
 
+  generic-names@4.0.0:
+    dependencies:
+      loader-utils: 3.3.1
+
   get-caller-file@2.0.5: {}
 
   get-port-please@3.2.0: {}
@@ -6813,6 +6868,10 @@ snapshots:
 
   hyperdyperid@1.2.0: {}
 
+  icss-utils@5.1.0(postcss@8.5.8):
+    dependencies:
+      postcss: 8.5.8
+
   ignore@5.3.2: {}
 
   ignore@7.0.5: {}
@@ -6996,10 +7055,14 @@ snapshots:
     dependencies:
       uc.micro: 2.1.0
 
+  loader-utils@3.3.1: {}
+
   locate-path@6.0.0:
     dependencies:
       p-locate: 5.0.0
 
+  lodash.camelcase@4.3.0: {}
+
   lodash.merge@4.6.2: {}
 
   longest-streak@3.1.0: {}
@@ -7642,6 +7705,39 @@ snapshots:
       postcss: 8.5.8
       yaml: 2.8.2
 
+  postcss-modules-extract-imports@3.1.0(postcss@8.5.8):
+    dependencies:
+      postcss: 8.5.8
+
+  postcss-modules-local-by-default@4.2.0(postcss@8.5.8):
+    dependencies:
+      icss-utils: 5.1.0(postcss@8.5.8)
+      postcss: 8.5.8
+      postcss-selector-parser: 7.1.1
+      postcss-value-parser: 4.2.0
+
+  postcss-modules-scope@3.2.1(postcss@8.5.8):
+    dependencies:
+      postcss: 8.5.8
+      postcss-selector-parser: 7.1.1
+
+  postcss-modules-values@4.0.0(postcss@8.5.8):
+    dependencies:
+      icss-utils: 5.1.0(postcss@8.5.8)
+      postcss: 8.5.8
+
+  postcss-modules@6.0.1(postcss@8.5.8):
+    dependencies:
+      generic-names: 4.0.0
+      icss-utils: 5.1.0(postcss@8.5.8)
+      lodash.camelcase: 4.3.0
+      postcss: 8.5.8
+      postcss-modules-extract-imports: 3.1.0(postcss@8.5.8)
+      postcss-modules-local-by-default: 4.2.0(postcss@8.5.8)
+      postcss-modules-scope: 3.2.1(postcss@8.5.8)
+      postcss-modules-values: 4.0.0(postcss@8.5.8)
+      string-hash: 1.1.3
+
   postcss-selector-parser@7.1.1:
     dependencies:
       cssesc: 3.0.0
@@ -8006,6 +8102,8 @@ snapshots:
 
   std-env@4.0.0: {}
 
+  string-hash@1.1.3: {}
+
   string-width@4.2.3:
     dependencies:
       emoji-regex: 8.0.0
@@ -8265,14 +8363,14 @@ snapshots:
       pathe: 2.0.3
       picomatch: 4.0.3
 
-  unplugin-vue@7.1.1(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(vue@3.5.30(typescript@5.9.3))(yaml@2.8.2):
+  unplugin-vue@7.1.1(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(vue@3.5.30(typescript@5.9.3))(yaml@2.8.2):
     dependencies:
       '@jridgewell/gen-mapping': 0.3.13
       '@jridgewell/trace-mapping': 0.3.31
       '@vue/reactivity': 3.5.30
       obug: 2.1.1
       unplugin: 3.0.0
-      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
+      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
       vue: 3.5.30(typescript@5.9.3)
     transitivePeerDependencies:
       - '@types/node'
@@ -8348,7 +8446,7 @@ snapshots:
       '@types/unist': 3.0.3
       vfile-message: 4.0.3
 
-  vite@8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2):
+  vite@8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2):
     dependencies:
       '@oxc-project/runtime': 0.115.0
       lightningcss: 1.32.0
@@ -8365,13 +8463,13 @@ snapshots:
       sass-embedded: 1.98.0
       yaml: 2.8.2
 
-  vitepress-plugin-group-icons@1.7.1(vite@8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)):
+  vitepress-plugin-group-icons@1.7.1(vite@8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)):
     dependencies:
       '@iconify-json/logos': 1.2.10
       '@iconify-json/vscode-icons': 1.2.45
       '@iconify/utils': 3.1.0
     optionalDependencies:
-      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
+      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
 
   vitepress-plugin-llms@1.11.0:
     dependencies:
@@ -8402,7 +8500,7 @@ snapshots:
       '@shikijs/transformers': 3.23.0
       '@shikijs/types': 3.23.0
       '@types/markdown-it': 14.1.2
-      '@vitejs/plugin-vue': 6.0.5(vite@8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2))(vue@3.5.30(typescript@5.9.3))
+      '@vitejs/plugin-vue': 6.0.5(vite@8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2))(vue@3.5.30(typescript@5.9.3))
       '@vue/devtools-api': 8.1.0
       '@vue/shared': 3.5.30
       '@vueuse/core': 14.2.1(vue@3.5.30(typescript@5.9.3))
@@ -8411,7 +8509,7 @@ snapshots:
       mark.js: 8.11.1
       minisearch: 7.2.0
       shiki: 3.23.0
-      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
+      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
       vue: 3.5.30(typescript@5.9.3)
     optionalDependencies:
       oxc-minify: 0.119.0
@@ -8462,7 +8560,7 @@ snapshots:
       tinyexec: 1.0.4
       tinyglobby: 0.2.15
       tinyrainbow: 3.1.0
-      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0)(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
+      vite: 8.0.0(@types/node@25.5.0)(@vitejs/devtools@0.1.0(@pnpm/logger@1001.0.1)(typescript@5.9.3)(vite@8.0.0)(vue@3.5.30(typescript@5.9.3)))(jiti@2.6.1)(sass-embedded@1.98.0)(sass@1.98.0)(yaml@2.8.2)
       why-is-node-running: 2.3.0
     optionalDependencies:
       '@types/node': 25.5.0
diff --git a/skills/tsdown/SKILL.md b/skills/tsdown/SKILL.md
index 356130a8e..f58fa1e26 100644
--- a/skills/tsdown/SKILL.md
+++ b/skills/tsdown/SKILL.md
@@ -96,7 +96,8 @@ export default defineConfig({
 | Shims | `shims: true` - Add ESM/CJS compatibility | [option-shims](references/option-shims.md) |
 | CJS default | `cjsDefault: true` (default) / `false` | [option-cjs-default](references/option-cjs-default.md) |
 | Package exports | `exports: true` - Auto-generate exports field | [option-package-exports](references/option-package-exports.md) |
-| CSS handling | **[experimental]** `css: { ... }` — full pipeline with preprocessors, Lightning CSS, PostCSS, code splitting; requires `@tsdown/css` | [option-css](references/option-css.md) |
+| CSS handling | **[experimental]** `css: { ... }` — full pipeline with preprocessors, Lightning CSS, PostCSS, CSS modules, code splitting; requires `@tsdown/css` | [option-css](references/option-css.md) |
+| CSS modules | `css: { modules: { localsConvention: 'camelCase' } }` — scoped class names for `.module.css` files | [option-css](references/option-css.md) |
 | CSS inject | `css: { inject: true }` — preserve CSS imports in JS output | [option-css](references/option-css.md) |
 | Unbundle mode | `unbundle: true` - Preserve directory structure | [option-unbundle](references/option-unbundle.md) |
 | Root directory | `root: 'src'` - Control output directory mapping | [option-root](references/option-root.md) |
diff --git a/skills/tsdown/references/option-css.md b/skills/tsdown/references/option-css.md
index 72799e176..4a0c692db 100644
--- a/skills/tsdown/references/option-css.md
+++ b/skills/tsdown/references/option-css.md
@@ -197,6 +197,37 @@ export default defineConfig({
 
 `css.lightningcss.targets` takes precedence over both `target` and `css.target` for CSS.
 
+## CSS Modules
+
+Files with `.module.css` (and `.module.scss`, `.module.less`, etc.) are treated as CSS modules — class names are scoped and exported as JS:
+
+```ts
+import styles from './app.module.css'
+console.log(styles.title) // "scoped_title_hash"
+```
+
+### Configuration
+
+```ts
+export default defineConfig({
+  css: {
+    modules: {
+      scopeBehaviour: 'local',             // 'local' (default) | 'global'
+      generateScopedName: '[hash]_[local]', // Lightning CSS pattern string
+      localsConvention: 'camelCase',       // 'camelCase' | 'camelCaseOnly' | 'dashes' | 'dashesOnly'
+    },
+  },
+})
+```
+
+Set `css.modules: false` to disable. Function-form `generateScopedName` requires `transformer: 'postcss'`.
+
+### Optional Dependencies (PostCSS path)
+
+```bash
+npm install -D postcss postcss-modules
+```
+
 ## Code Splitting
 
 ### Merged (Default)
@@ -233,6 +264,22 @@ export default defineConfig({
 })
 ```
 
+## PostCSS Optional Peer Dependencies
+
+When using `transformer: 'postcss'`, install these as needed:
+
+| Package | Purpose | Required When |
+|---------|---------|---------------|
+| `postcss` | Core PostCSS engine | Always (with `transformer: 'postcss'`) |
+| `postcss-import` | Resolve/inline `@import` | CSS uses `@import` |
+| `postcss-modules` | CSS modules (scoped classes) | Using `.module.css` files |
+
+```bash
+npm install -D postcss postcss-import postcss-modules
+```
+
+All declared as optional peer dependencies of `@tsdown/css`.
+
 ## Options Reference
 
 | Option | Type | Default | Description |
@@ -241,6 +288,7 @@ export default defineConfig({
 | `css.splitting` | `boolean` | `false` | Per-chunk CSS splitting |
 | `css.fileName` | `string` | `'style.css'` | Merged CSS file name |
 | `css.minify` | `boolean` | `false` | CSS minification |
+| `css.modules` | `object \| false` | `{}` | CSS modules config, or `false` to disable |
 | `css.inject` | `boolean` | `false` | Preserve CSS imports in JS output |
 | `css.target` | `string \| string[] \| false` | _from `target`_ | CSS-specific lowering target |
 | `css.postcss` | `string \| object` | — | PostCSS config path or inline options |
diff --git a/tests/__snapshots__/css-modules/basic-css-module-exports-scoped-class-names.snap.md b/tests/__snapshots__/css-modules/basic-css-module-exports-scoped-class-names.snap.md
new file mode 100644
index 000000000..7d9281c09
--- /dev/null
+++ b/tests/__snapshots__/css-modules/basic-css-module-exports-scoped-class-names.snap.md
@@ -0,0 +1,25 @@
+## index.mjs
+
+```mjs
+//#region app.module.css
+var app_module_default = {
+	"content": "mod_content",
+	"title": "mod_title"
+};
+//#endregion
+export { app_module_default as styles };
+
+```
+
+## style.css
+
+```css
+.mod_title {
+  color: red;
+}
+
+.mod_content {
+  font-size: 14px;
+}
+
+```
diff --git a/tests/__snapshots__/css-modules/css-module-with-modules-false-disables-scoping.snap.md b/tests/__snapshots__/css-modules/css-module-with-modules-false-disables-scoping.snap.md
new file mode 100644
index 000000000..1845f3339
--- /dev/null
+++ b/tests/__snapshots__/css-modules/css-module-with-modules-false-disables-scoping.snap.md
@@ -0,0 +1,15 @@
+## index.mjs
+
+```mjs
+export {};
+
+```
+
+## style.css
+
+```css
+.title {
+  color: red;
+}
+
+```
diff --git a/tests/__snapshots__/css-modules/css-module-with-splitting.snap.md b/tests/__snapshots__/css-modules/css-module-with-splitting.snap.md
new file mode 100644
index 000000000..f0cfb93d2
--- /dev/null
+++ b/tests/__snapshots__/css-modules/css-module-with-splitting.snap.md
@@ -0,0 +1,18 @@
+## index.css
+
+```css
+.mod_title {
+  color: red;
+}
+
+```
+
+## index.mjs
+
+```mjs
+//#region app.module.css
+var app_module_default = { "title": "mod_title" };
+//#endregion
+export { app_module_default as styles };
+
+```
diff --git a/tests/__snapshots__/css-modules/non-module-css-is-not-affected.snap.md b/tests/__snapshots__/css-modules/non-module-css-is-not-affected.snap.md
new file mode 100644
index 000000000..1845f3339
--- /dev/null
+++ b/tests/__snapshots__/css-modules/non-module-css-is-not-affected.snap.md
@@ -0,0 +1,15 @@
+## index.mjs
+
+```mjs
+export {};
+
+```
+
+## style.css
+
+```css
+.title {
+  color: red;
+}
+
+```
diff --git a/tests/css.test.ts b/tests/css.test.ts
index 294d20038..62ba2037f 100644
--- a/tests/css.test.ts
+++ b/tests/css.test.ts
@@ -1572,4 +1572,80 @@ describe('css', () => {
       expect(asyncBCode).not.toContain('.mjs"')
     })
   })
+
+  describe('css modules', () => {
+    test('basic css module exports scoped class names', async (context) => {
+      const { fileMap, outputFiles } = await testBuild({
+        context,
+        files: {
+          'index.ts': `export { default as styles } from './app.module.css'`,
+          'app.module.css': `.title { color: red }\n.content { font-size: 14px }`,
+        },
+        options: {
+          css: { modules: { generateScopedName: 'mod_[local]' } },
+        },
+      })
+      expect(outputFiles).toContain('style.css')
+      expect(outputFiles).toContain('index.mjs')
+
+      const js = fileMap['index.mjs']
+      expect(js).toContain('export')
+      expect(js).toContain('mod_title')
+      expect(js).toContain('mod_content')
+
+      const css = fileMap['style.css']
+      expect(css).toContain('.mod_title')
+      expect(css).toContain('.mod_content')
+      expect(css).not.toMatch(/(?<!_)\.title\b/)
+      expect(css).not.toMatch(/(?<!_)\.content\b/)
+    })
+
+    test('css module with modules=false disables scoping', async (context) => {
+      const { fileMap } = await testBuild({
+        context,
+        files: {
+          'index.ts': `import './app.module.css'`,
+          'app.module.css': `.title { color: red }`,
+        },
+        options: {
+          css: { modules: false },
+        },
+      })
+      const css = fileMap['style.css']
+      expect(css).toContain('.title')
+    })
+
+    test('non-module css is not affected', async (context) => {
+      const { fileMap } = await testBuild({
+        context,
+        files: {
+          'index.ts': `import './app.css'`,
+          'app.css': `.title { color: red }`,
+        },
+      })
+      const css = fileMap['style.css']
+      expect(css).toContain('.title')
+    })
+
+    test('css module with splitting', async (context) => {
+      const { fileMap, outputFiles } = await testBuild({
+        context,
+        files: {
+          'index.ts': `export { default as styles } from './app.module.css'`,
+          'app.module.css': `.title { color: red }`,
+        },
+        options: {
+          css: {
+            splitting: true,
+            modules: { generateScopedName: 'mod_[local]' },
+          },
+        },
+      })
+      expect(outputFiles).toContain('index.css')
+      expect(outputFiles).toContain('index.mjs')
+
+      const js = fileMap['index.mjs']
+      expect(js).toContain('mod_title')
+    })
+  })
 })