diff --git a/bun.lockb b/bun.lockb
index 9c7d85d..0cf56fd 100755
Binary files a/bun.lockb and b/bun.lockb differ
diff --git a/package.json b/package.json
index d42c720..edcdc71 100644
--- a/package.json
+++ b/package.json
@@ -79,12 +79,14 @@
   },
   "devDependencies": {
     "@types/node": "^20.6.0",
+    "@types/supertest": "^2.0.12",
     "@vitest/coverage-v8": "^0.34.4",
     "bumpp": "^9.2.0",
     "cookie-es": "^1.0.0",
     "gh-changelogen": "^0.2.8",
     "h3": "^1.8.1",
     "lint-staged": "^14.0.0",
+    "supertest": "^6.3.3",
     "typescript": "^5.2.2",
     "unbuild": "^2.0.0",
     "vitest": "^0.34.4"
diff --git a/src/h3.test.ts b/src/h3.test.ts
index 99f07d5..495c981 100644
--- a/src/h3.test.ts
+++ b/src/h3.test.ts
@@ -1,8 +1,16 @@
-import { describe, expect, test } from 'vitest'
-import { getAcceptLanguages, getCookieLocale, getLocale } from './h3.ts'
+import { beforeEach, describe, expect, test } from 'vitest'
+import { createApp, eventHandler, toNodeListener } from 'h3'
+import supertest from 'supertest'
+import {
+  getAcceptLanguages,
+  getCookieLocale,
+  getLocale,
+  setCookieLocale,
+} from './h3.ts'
 import { DEFAULT_COOKIE_NAME, DEFAULT_LANG_TAG } from './constants.ts'
 
-import type { H3Event } from 'h3'
+import type { App, H3Event } from 'h3'
+import type { SuperTest, Test } from 'supertest'
 
 describe('getAcceptLanguages', () => {
   test('basic', () => {
@@ -192,3 +200,70 @@ describe('getCookieLocale', () => {
       .toThrowError(RangeError)
   })
 })
+
+describe('setCookieLocale', () => {
+  let app: App
+  let request: SuperTest<Test>
+
+  beforeEach(() => {
+    app = createApp({ debug: false })
+    request = supertest(toNodeListener(app))
+  })
+
+  test('specify Locale instance', async () => {
+    app.use(
+      '/',
+      eventHandler((event) => {
+        const locale = new Intl.Locale('ja-JP')
+        setCookieLocale(event, locale)
+        return '200'
+      }),
+    )
+    const result = await request.get('/')
+    expect(result.headers['set-cookie']).toEqual([
+      'i18n_locale=ja-JP; Path=/',
+    ])
+  })
+
+  test('specify language tag', async () => {
+    app.use(
+      '/',
+      eventHandler((event) => {
+        setCookieLocale(event, 'ja-JP')
+        return '200'
+      }),
+    )
+    const result = await request.get('/')
+    expect(result.headers['set-cookie']).toEqual([
+      'i18n_locale=ja-JP; Path=/',
+    ])
+  })
+
+  test('specify cookie name', async () => {
+    app.use(
+      '/',
+      eventHandler((event) => {
+        setCookieLocale(event, 'ja-JP', { name: 'intlify_locale' })
+        return '200'
+      }),
+    )
+    const result = await request.get('/')
+    expect(result.headers['set-cookie']).toEqual([
+      'intlify_locale=ja-JP; Path=/',
+    ])
+  })
+
+  test('Syntax Error', () => {
+    const eventMock = {
+      node: {
+        req: {
+          method: 'GET',
+          headers: {},
+        },
+      },
+    } as H3Event
+
+    expect(() => setCookieLocale(eventMock, 'j'))
+      .toThrowError(/locale is invalid: j/)
+  })
+})
diff --git a/src/h3.ts b/src/h3.ts
index 0a17d57..afc77eb 100644
--- a/src/h3.ts
+++ b/src/h3.ts
@@ -1,8 +1,13 @@
-import { getAcceptLanguagesWithGetter, getLocaleWithGetter } from './http.ts'
-import { getCookie, getHeaders } from 'h3'
+import {
+  getAcceptLanguagesWithGetter,
+  getLocaleWithGetter,
+  validateLocale,
+} from './http.ts'
+import { getCookie, getHeaders, setCookie } from 'h3'
 import { DEFAULT_COOKIE_NAME, DEFAULT_LANG_TAG } from './constants.ts'
 
 import type { H3Event } from 'h3'
+import type { CookieOptions } from './http.ts'
 
 /**
  * get accpet languages
@@ -97,3 +102,34 @@ export function getCookieLocale(
 ): Intl.Locale {
   return getLocaleWithGetter(() => getCookie(event, name) || lang)
 }
+
+/**
+ * set locale to the response `Set-Cookie` header.
+ *
+ * @example
+ * example for h3:
+ *
+ * ```ts
+ * import { createApp, eventHandler } from 'h3'
+ * import { getCookieLocale } from '@intlify/utils/h3'
+ *
+ * app.use(eventHandler(event) => {
+ *   setCookieLocale(event, 'ja-JP')
+ *   // ...
+ * })
+ * ```
+ *
+ * @param {H3Event} event The {@link H3Event | H3} event
+ * @param {string | Intl.Locale} locale The locale value
+ * @param {CookieOptions} options The cookie options, `name` option is `i18n_locale` as default, and `path` option is `/` as default.
+ *
+ * @throws {SyntaxError} Throws the {@link SyntaxError} if `locale` is invalid.
+ */
+export function setCookieLocale(
+  event: H3Event,
+  locale: string | Intl.Locale,
+  options: CookieOptions = { name: DEFAULT_COOKIE_NAME, path: '/' },
+): void {
+  validateLocale(locale)
+  setCookie(event, options.name!, locale.toString(), options)
+}
diff --git a/src/http.ts b/src/http.ts
index 48ae9ed..0a9e742 100644
--- a/src/http.ts
+++ b/src/http.ts
@@ -1,4 +1,107 @@
 import { parseAcceptLanguage } from './shared.ts'
+import { isLocale, validateLanguageTag } from './shared.ts'
+
+// import type { CookieSerializeOptions } from 'cookie-es'
+// NOTE: This is a copy of the type definition from `cookie-es` package, we want to avoid building error for this type definition ...
+
+interface CookieSerializeOptions {
+  /**
+   * Specifies the value for the {@link https://tools.ietf.org/html/rfc6265#section-5.2.3|Domain Set-Cookie attribute}. By default, no
+   * domain is set, and most clients will consider the cookie to apply to only
+   * the current domain.
+   */
+  domain?: string | undefined
+  /**
+   * Specifies a function that will be used to encode a cookie's value. Since
+   * value of a cookie has a limited character set (and must be a simple
+   * string), this function can be used to encode a value into a string suited
+   * for a cookie's value.
+   *
+   * The default function is the global `encodeURIComponent`, which will
+   * encode a JavaScript string into UTF-8 byte sequences and then URL-encode
+   * any that fall outside of the cookie range.
+   */
+  encode?(value: string): string
+  /**
+   * Specifies the `Date` object to be the value for the {@link https://tools.ietf.org/html/rfc6265#section-5.2.1|`Expires` `Set-Cookie` attribute}. By default,
+   * no expiration is set, and most clients will consider this a "non-persistent cookie" and will delete
+   * it on a condition like exiting a web browser application.
+   *
+   * *Note* the {@link https://tools.ietf.org/html/rfc6265#section-5.3|cookie storage model specification}
+   * states that if both `expires` and `maxAge` are set, then `maxAge` takes precedence, but it is
+   * possible not all clients by obey this, so if both are set, they should
+   * point to the same date and time.
+   */
+  expires?: Date | undefined
+  /**
+   * Specifies the boolean value for the {@link https://tools.ietf.org/html/rfc6265#section-5.2.6|`HttpOnly` `Set-Cookie` attribute}.
+   * When truthy, the `HttpOnly` attribute is set, otherwise it is not. By
+   * default, the `HttpOnly` attribute is not set.
+   *
+   * *Note* be careful when setting this to true, as compliant clients will
+   * not allow client-side JavaScript to see the cookie in `document.cookie`.
+   */
+  httpOnly?: boolean | undefined
+  /**
+   * Specifies the number (in seconds) to be the value for the `Max-Age`
+   * `Set-Cookie` attribute. The given number will be converted to an integer
+   * by rounding down. By default, no maximum age is set.
+   *
+   * *Note* the {@link https://tools.ietf.org/html/rfc6265#section-5.3|cookie storage model specification}
+   * states that if both `expires` and `maxAge` are set, then `maxAge` takes precedence, but it is
+   * possible not all clients by obey this, so if both are set, they should
+   * point to the same date and time.
+   */
+  maxAge?: number | undefined
+  /**
+   * Specifies the value for the {@link https://tools.ietf.org/html/rfc6265#section-5.2.4|`Path` `Set-Cookie` attribute}.
+   * By default, the path is considered the "default path".
+   */
+  path?: string | undefined
+  /**
+   * Specifies the `string` to be the value for the [`Priority` `Set-Cookie` attribute][rfc-west-cookie-priority-00-4.1].
+   *
+   * - `'low'` will set the `Priority` attribute to `Low`.
+   * - `'medium'` will set the `Priority` attribute to `Medium`, the default priority when not set.
+   * - `'high'` will set the `Priority` attribute to `High`.
+   *
+   * More information about the different priority levels can be found in
+   * [the specification][rfc-west-cookie-priority-00-4.1].
+   *
+   * **note** This is an attribute that has not yet been fully standardized, and may change in the future.
+   * This also means many clients may ignore this attribute until they understand it.
+   */
+  priority?: 'low' | 'medium' | 'high' | undefined
+  /**
+   * Specifies the boolean or string to be the value for the {@link https://tools.ietf.org/html/draft-ietf-httpbis-rfc6265bis-03#section-4.1.2.7|`SameSite` `Set-Cookie` attribute}.
+   *
+   * - `true` will set the `SameSite` attribute to `Strict` for strict same
+   * site enforcement.
+   * - `false` will not set the `SameSite` attribute.
+   * - `'lax'` will set the `SameSite` attribute to Lax for lax same site
+   * enforcement.
+   * - `'strict'` will set the `SameSite` attribute to Strict for strict same
+   * site enforcement.
+   *  - `'none'` will set the SameSite attribute to None for an explicit
+   *  cross-site cookie.
+   *
+   * More information about the different enforcement levels can be found in {@link https://tools.ietf.org/html/draft-ietf-httpbis-rfc6265bis-03#section-4.1.2.7|the specification}.
+   *
+   * *note* This is an attribute that has not yet been fully standardized, and may change in the future. This also means many clients may ignore this attribute until they understand it.
+   */
+  sameSite?: true | false | 'lax' | 'strict' | 'none' | undefined
+  /**
+   * Specifies the boolean value for the {@link https://tools.ietf.org/html/rfc6265#section-5.2.5|`Secure` `Set-Cookie` attribute}. When truthy, the
+   * `Secure` attribute is set, otherwise it is not. By default, the `Secure` attribute is not set.
+   *
+   * *Note* be careful when setting this to `true`, as compliant clients will
+   * not send the cookie back to the server in the future if the browser does
+   * not have an HTTPS connection.
+   */
+  secure?: boolean | undefined
+}
+
+export type CookieOptions = CookieSerializeOptions & { name?: string }
 
 export function getAcceptLanguagesWithGetter(
   getter: () => string | null | undefined,
@@ -10,3 +113,26 @@ export function getAcceptLanguagesWithGetter(
 export function getLocaleWithGetter(getter: () => string): Intl.Locale {
   return new Intl.Locale(getter())
 }
+
+export function validateLocale(locale: string | Intl.Locale): void {
+  if (
+    !(isLocale(locale) ||
+      typeof locale === 'string' && validateLanguageTag(locale))
+  ) {
+    throw new SyntaxError(`locale is invalid: ${locale.toString()}`)
+  }
+}
+
+export function getExistCookies(
+  name: string,
+  getter: () => unknown,
+) {
+  let setCookies = getter()
+  if (!Array.isArray(setCookies)) {
+    setCookies = [setCookies]
+  }
+  setCookies = (setCookies as string[]).filter((cookieValue: string) =>
+    cookieValue && !cookieValue.startsWith(name + '=')
+  )
+  return setCookies as string[]
+}
diff --git a/src/node.test.ts b/src/node.test.ts
index c5f62dc..3f89609 100644
--- a/src/node.test.ts
+++ b/src/node.test.ts
@@ -1,6 +1,12 @@
 import { describe, expect, test } from 'vitest'
-import { getAcceptLanguages, getCookieLocale, getLocale } from './node.ts'
-import { IncomingMessage } from 'node:http'
+import supertest from 'supertest'
+import {
+  getAcceptLanguages,
+  getCookieLocale,
+  getLocale,
+  setCookieLocale,
+} from './node.ts'
+import { createServer, IncomingMessage, OutgoingMessage } from 'node:http'
 import { DEFAULT_COOKIE_NAME, DEFAULT_LANG_TAG } from './constants.ts'
 
 describe('getAcceptLanguages', () => {
@@ -132,3 +138,52 @@ describe('getCookieLocale', () => {
       .toThrowError(RangeError)
   })
 })
+
+describe('setCookieLocale', () => {
+  test('specify Locale instance', async () => {
+    const server = createServer((_req, res) => {
+      const locale = new Intl.Locale('ja-JP')
+      setCookieLocale(res, locale)
+      res.writeHead(200)
+      res.end('hello world!')
+    })
+    const request = supertest(server)
+    const result = await request.get('/')
+    expect(result.headers['set-cookie']).toEqual([
+      `${DEFAULT_COOKIE_NAME}=ja-JP; Path=/`,
+    ])
+  })
+
+  test('specify language tag', async () => {
+    const server = createServer((_req, res) => {
+      setCookieLocale(res, 'ja-JP')
+      res.writeHead(200)
+      res.end('hello world!')
+    })
+    const request = supertest(server)
+    const result = await request.get('/')
+    expect(result.headers['set-cookie']).toEqual([
+      `${DEFAULT_COOKIE_NAME}=ja-JP; Path=/`,
+    ])
+  })
+
+  test('specify cookie name', async () => {
+    const server = createServer((_req, res) => {
+      setCookieLocale(res, 'ja-JP', { name: 'intlify_locale' })
+      res.writeHead(200)
+      res.end('hello world!')
+    })
+    const request = supertest(server)
+    const result = await request.get('/')
+    expect(result.headers['set-cookie']).toEqual([
+      'intlify_locale=ja-JP; Path=/',
+    ])
+  })
+
+  test('Syntax Error', () => {
+    const mockRes = {} as OutgoingMessage
+
+    expect(() => setCookieLocale(mockRes, 'j'))
+      .toThrowError(/locale is invalid: j/)
+  })
+})
diff --git a/src/node.ts b/src/node.ts
index 6bbad1b..af28ba3 100644
--- a/src/node.ts
+++ b/src/node.ts
@@ -1,8 +1,15 @@
-import { IncomingMessage } from 'node:http'
-import { parse } from 'cookie-es'
-import { getAcceptLanguagesWithGetter, getLocaleWithGetter } from './http.ts'
+import { IncomingMessage, OutgoingMessage } from 'node:http'
+import { parse, serialize } from 'cookie-es'
+import {
+  getAcceptLanguagesWithGetter,
+  getExistCookies,
+  getLocaleWithGetter,
+  validateLocale,
+} from './http.ts'
 import { DEFAULT_COOKIE_NAME, DEFAULT_LANG_TAG } from './constants.ts'
 
+import type { CookieOptions } from './http.ts'
+
 /**
  * get accpet languages
  *
@@ -97,3 +104,42 @@ export function getCookieLocale(
   }
   return getLocaleWithGetter(getter)
 }
+
+/**
+ * set locale to the response `Set-Cookie` header.
+ *
+ * @example
+ * example for Node.js response:
+ *
+ * ```ts
+ * import { createServer } from 'node:http'
+ * import { setCookieLocale } from '@intlify/utils/node'
+ *
+ * const server = createServer((req, res) => {
+ *   setCookieLocale(res, 'ja-JP')
+ *   // ...
+ * })
+ * ```
+ *
+ * @param {OutgoingMessage} res The {@link OutgoingMessage | response}
+ * @param {string | Intl.Locale} locale The locale value
+ * @param {CookieOptions} options The cookie options, `name` option is `i18n_locale` as default, and `path` option is `/` as default.
+ *
+ * @throws {SyntaxError} Throws the {@link SyntaxError} if `locale` is invalid.
+ */
+export function setCookieLocale(
+  res: OutgoingMessage,
+  locale: string | Intl.Locale,
+  options: CookieOptions = { name: DEFAULT_COOKIE_NAME },
+): void {
+  validateLocale(locale)
+  const setCookies = getExistCookies(
+    options.name!,
+    () => res.getHeader('set-cookie'),
+  )
+  const target = serialize(options.name!, locale.toString(), {
+    path: '/',
+    ...options,
+  })
+  res.setHeader('set-cookie', [...setCookies, target])
+}
diff --git a/src/web.test.ts b/src/web.test.ts
index e9df43d..d5ddb1c 100644
--- a/src/web.test.ts
+++ b/src/web.test.ts
@@ -1,5 +1,10 @@
 import { describe, expect, test } from 'vitest'
-import { getAcceptLanguages, getCookieLocale, getLocale } from './web.ts'
+import {
+  getAcceptLanguages,
+  getCookieLocale,
+  getLocale,
+  setCookieLocale,
+} from './web.ts'
 import { DEFAULT_COOKIE_NAME, DEFAULT_LANG_TAG } from './constants.ts'
 
 describe('getAcceptLanguages', () => {
@@ -96,3 +101,36 @@ describe('getCookieLocale', () => {
       .toThrowError(RangeError)
   })
 })
+
+describe('setCookieLocale', () => {
+  test('specify Locale instance', () => {
+    const res = new Response('hello world!')
+    const locale = new Intl.Locale('ja-JP')
+    setCookieLocale(res, locale)
+    expect(res.headers.getSetCookie()).toEqual([
+      `${DEFAULT_COOKIE_NAME}=ja-JP; Path=/`,
+    ])
+  })
+
+  test('specify language tag', () => {
+    const res = new Response('hello world!')
+    setCookieLocale(res, 'ja-JP')
+    expect(res.headers.getSetCookie()).toEqual([
+      `${DEFAULT_COOKIE_NAME}=ja-JP; Path=/`,
+    ])
+  })
+
+  test('specify cookie name', () => {
+    const res = new Response('hello world!')
+    setCookieLocale(res, 'ja-JP', { name: 'intlify_locale' })
+    expect(res.headers.getSetCookie()).toEqual([
+      'intlify_locale=ja-JP; Path=/',
+    ])
+  })
+
+  test('Syntax Error', () => {
+    const res = new Response('hello world!')
+    expect(() => setCookieLocale(res, 'j'))
+      .toThrowError(/locale is invalid: j/)
+  })
+})
diff --git a/src/web.ts b/src/web.ts
index 553f9de..382cb45 100644
--- a/src/web.ts
+++ b/src/web.ts
@@ -1,7 +1,14 @@
-import { parse } from 'cookie-es'
-import { getAcceptLanguagesWithGetter, getLocaleWithGetter } from './http.ts'
+import { parse, serialize } from 'cookie-es'
+import {
+  getAcceptLanguagesWithGetter,
+  getExistCookies,
+  getLocaleWithGetter,
+  validateLocale,
+} from './http.ts'
 import { DEFAULT_COOKIE_NAME, DEFAULT_LANG_TAG } from './constants.ts'
 
+import type { CookieOptions } from './http.ts'
+
 /**
  * get accpet languages
  *
@@ -96,3 +103,46 @@ export function getCookieLocale(
   }
   return getLocaleWithGetter(getter)
 }
+
+/**
+ * set locale to the response `Set-Cookie` header.
+ *
+ * @example
+ * example for Web API response on Bun:
+ *
+ * ```ts
+ * import { setCookieLocale } from '@intlify/utils/web'
+ *
+ * Bun.serve({
+ *   port: 8080,
+ *   fetch(req) {
+ *     const res = new Response('こんにちは、世界！')
+ *     setCookieLocale(res, 'ja-JP')
+ *     // ...
+ *     return res
+ *   },
+ * })
+ * ```
+ *
+ * @param {Response} res The {@link Response | response}
+ * @param {string | Intl.Locale} locale The locale value
+ * @param {CookieOptions} options The cookie options, `name` option is `i18n_locale` as default, and `path` option is `/` as default.
+ *
+ * @throws {SyntaxError} Throws the {@link SyntaxError} if `locale` is invalid.
+ */
+export function setCookieLocale(
+  res: Response,
+  locale: string | Intl.Locale,
+  options: CookieOptions = { name: DEFAULT_COOKIE_NAME },
+): void {
+  validateLocale(locale)
+  const setCookies = getExistCookies(
+    options.name!,
+    () => res.headers.getSetCookie(),
+  )
+  const target = serialize(options.name!, locale.toString(), {
+    path: '/',
+    ...options,
+  })
+  res.headers.set('set-cookie', [...setCookies, target].join('; '))
+}