diff --git a/packages/vite/src/client/client.ts b/packages/vite/src/client/client.ts
index e75c439dd1bfa7..747c2df86e477c 100644
--- a/packages/vite/src/client/client.ts
+++ b/packages/vite/src/client/client.ts
@@ -289,7 +289,10 @@ async function handleMessage(payload: HotPayload) {
       }
       await activeHmrClient.notifyListeners('vite:beforeFullReload', payload)
       if (hasDocument) {
-        if (payload.path && payload.path.endsWith('.html')) {
+        if (
+          payload.path &&
+          (payload.path.endsWith('.html') || payload.path.endsWith('.htm'))
+        ) {
           // if html file is edited, only reload the page if the browser is
           // currently on that page.
           const pagePath = decodeURI(location.pathname)
diff --git a/packages/vite/src/node/build.ts b/packages/vite/src/node/build.ts
index b61689a1cd05f6..ee76670f79b51e 100644
--- a/packages/vite/src/node/build.ts
+++ b/packages/vite/src/node/build.ts
@@ -624,7 +624,11 @@ export function resolveRolldownOptions(
       : options.rolldownOptions.input ||
         (topLevelInput ?? resolve('index.html'))
 
-  if (ssr && typeof input === 'string' && input.endsWith('.html')) {
+  if (
+    ssr &&
+    typeof input === 'string' &&
+    (input.endsWith('.html') || input.endsWith('.htm'))
+  ) {
     throw new Error(
       `rolldownOptions.input should not be an html file when building for SSR. ` +
         `Please specify a dedicated SSR entry.`,
diff --git a/packages/vite/src/node/optimizer/scan.ts b/packages/vite/src/node/optimizer/scan.ts
index 812db849877819..8d42acf7de34be 100644
--- a/packages/vite/src/node/optimizer/scan.ts
+++ b/packages/vite/src/node/optimizer/scan.ts
@@ -457,7 +457,7 @@ function rolldownScanPlugin(
     let raw = await fsp.readFile(id, 'utf-8')
     // Avoid matching the content of the comment
     raw = raw.replace(commentRE, '<!---->')
-    const isHtml = id.endsWith('.html')
+    const isHtml = id.endsWith('.html') || id.endsWith('.htm')
     let js = ''
     let scriptId = 0
     const matches = raw.matchAll(scriptRE)
diff --git a/packages/vite/src/node/plugins/asset.ts b/packages/vite/src/node/plugins/asset.ts
index b7a0a1b3251bc8..dcc514aa3b0530 100644
--- a/packages/vite/src/node/plugins/asset.ts
+++ b/packages/vite/src/node/plugins/asset.ts
@@ -557,7 +557,7 @@ function shouldInline(
     if (buildPluginContext.getModuleInfo(id)?.isEntry) return false
   }
   if (forceInline !== undefined) return forceInline
-  if (file.endsWith('.html')) return false
+  if (file.endsWith('.html') || file.endsWith('.htm')) return false
   // Don't inline SVG with fragments, as they are meant to be reused
   if (file.endsWith('.svg') && id.includes('#')) return false
   let limit: number
diff --git a/packages/vite/src/node/plugins/html.ts b/packages/vite/src/node/plugins/html.ts
index 36dfafd4fca36b..09ac6e597b2824 100644
--- a/packages/vite/src/node/plugins/html.ts
+++ b/packages/vite/src/node/plugins/html.ts
@@ -436,7 +436,7 @@ export function buildHtmlPlugin(config: ResolvedConfig): Plugin {
     },
 
     transform: {
-      filter: { id: /\.html$/ },
+      filter: { id: /\.(?:html|htm)$/ },
       async handler(html, id) {
         id = normalizePath(id)
         const relativeUrlPath = normalizePath(path.relative(config.root, id))
diff --git a/packages/vite/src/node/plugins/resolve.ts b/packages/vite/src/node/plugins/resolve.ts
index aa454d43de0d0f..801cf00795b6d3 100644
--- a/packages/vite/src/node/plugins/resolve.ts
+++ b/packages/vite/src/node/plugins/resolve.ts
@@ -427,7 +427,8 @@ function optimizerResolvePlugin(
           ...resolveOptions,
           scan: resolveOpts.scan ?? resolveOptions.scan,
         }
-        options.preferRelative ||= importer?.endsWith('.html')
+        options.preferRelative ||=
+          importer?.endsWith('.html') || importer?.endsWith('.htm')
 
         // resolve pre-bundled deps requests, these could be resolved by
         // tryFileResolve or /fs/ resolution but these files may not yet
diff --git a/packages/vite/src/node/server/hmr.ts b/packages/vite/src/node/server/hmr.ts
index 84e9616b5d45f1..beb6d06c78418b 100644
--- a/packages/vite/src/node/server/hmr.ts
+++ b/packages/vite/src/node/server/hmr.ts
@@ -630,7 +630,10 @@ export async function handleHMRUpdate(
       }
       if (!options.modules.length) {
         // html file cannot be hot updated
-        if (file.endsWith('.html') && environment.name === 'client') {
+        if (
+          (file.endsWith('.html') || file.endsWith('.htm')) &&
+          environment.name === 'client'
+        ) {
           environment.logger.info(
             colors.green(`page reload `) + colors.dim(shortFile),
             {
@@ -747,7 +750,7 @@ export function updateModules(
 
   // html file cannot be hot updated because it may be used as the template for a top-level request response.
   const isClientHtmlChange =
-    file.endsWith('.html') &&
+    (file.endsWith('.html') || file.endsWith('.htm')) &&
     environment.name === 'client' &&
     // if the html file is imported as a module, we assume that this file is
     // not used as the template for top-level request response
diff --git a/packages/vite/src/node/server/middlewares/htmlFallback.ts b/packages/vite/src/node/server/middlewares/htmlFallback.ts
index 1ab4f5fc4c6a6f..22a42bb4ad45fe 100644
--- a/packages/vite/src/node/server/middlewares/htmlFallback.ts
+++ b/packages/vite/src/node/server/middlewares/htmlFallback.ts
@@ -49,25 +49,33 @@ export function htmlFallbackMiddleware(
       return next()
     }
 
-    // .html files are not handled by serveStaticMiddleware
+    // .html/.htm files are not handled by serveStaticMiddleware
     // so we need to check if the file exists
-    if (pathname.endsWith('.html')) {
+    if (pathname.endsWith('.html') || pathname.endsWith('.htm')) {
       if (checkFileExists(pathname)) {
         debug?.(`Rewriting ${req.method} ${req.url} to ${url}`)
         req.url = url
         return next()
       }
     }
-    // trailing slash should check for fallback index.html
+    // trailing slash should check for fallback index.html / index.htm
     else if (pathname.endsWith('/')) {
-      if (checkFileExists(joinUrlSegments(pathname, 'index.html'))) {
+      const indexHtml = joinUrlSegments(pathname, 'index.html')
+      const indexHtm = joinUrlSegments(pathname, 'index.htm')
+      if (checkFileExists(indexHtml)) {
         const newUrl = url + 'index.html'
         debug?.(`Rewriting ${req.method} ${req.url} to ${newUrl}`)
         req.url = newUrl
         return next()
       }
+      if (checkFileExists(indexHtm)) {
+        const newUrl = url + 'index.htm'
+        debug?.(`Rewriting ${req.method} ${req.url} to ${newUrl}`)
+        req.url = newUrl
+        return next()
+      }
     }
-    // non-trailing slash should check for fallback .html
+    // non-trailing slash should check for fallback .html / .htm
     else {
       if (checkFileExists(pathname + '.html')) {
         const newUrl = url + '.html'
@@ -75,6 +83,12 @@ export function htmlFallbackMiddleware(
         req.url = newUrl
         return next()
       }
+      if (checkFileExists(pathname + '.htm')) {
+        const newUrl = url + '.htm'
+        debug?.(`Rewriting ${req.method} ${req.url} to ${newUrl}`)
+        req.url = newUrl
+        return next()
+      }
     }
 
     if (spaFallback) {
diff --git a/packages/vite/src/node/server/middlewares/indexHtml.ts b/packages/vite/src/node/server/middlewares/indexHtml.ts
index ea734f41d0f03a..2c5acb98cd4532 100644
--- a/packages/vite/src/node/server/middlewares/indexHtml.ts
+++ b/packages/vite/src/node/server/middlewares/indexHtml.ts
@@ -463,7 +463,10 @@ export function indexHtmlMiddleware(
 
     const url = req.url && cleanUrl(req.url)
     // htmlFallbackMiddleware appends '.html' to URLs
-    if (url?.endsWith('.html') && req.headers['sec-fetch-dest'] !== 'script') {
+    if (
+      (url?.endsWith('.html') || url?.endsWith('.htm')) &&
+      req.headers['sec-fetch-dest'] !== 'script'
+    ) {
       if (fullBundle) {
         let pathname
         try {
diff --git a/packages/vite/src/node/server/middlewares/memoryFiles.ts b/packages/vite/src/node/server/middlewares/memoryFiles.ts
index 308d7b4a5d06ca..300386afc220ef 100644
--- a/packages/vite/src/node/server/middlewares/memoryFiles.ts
+++ b/packages/vite/src/node/server/middlewares/memoryFiles.ts
@@ -15,7 +15,7 @@ export function memoryFilesMiddleware(
 
   return function viteMemoryFilesMiddleware(req, res, next) {
     const cleanedUrl = cleanUrl(req.url!)
-    if (cleanedUrl.endsWith('.html')) {
+    if (cleanedUrl.endsWith('.html') || cleanedUrl.endsWith('.htm')) {
       return next()
     }
 
diff --git a/packages/vite/src/node/server/middlewares/static.ts b/packages/vite/src/node/server/middlewares/static.ts
index bb093f127f5d13..d901a9073a939a 100644
--- a/packages/vite/src/node/server/middlewares/static.ts
+++ b/packages/vite/src/node/server/middlewares/static.ts
@@ -143,6 +143,7 @@ export function serveStaticMiddleware(
     if (
       cleanedUrl.endsWith('/') ||
       path.extname(cleanedUrl) === '.html' ||
+      path.extname(cleanedUrl) === '.htm' ||
       isInternalRequest(req.url!) ||
       // skip url starting with // as these will be interpreted as
       // scheme relative URLs by new URL() and will not be a valid file path
diff --git a/packages/vite/src/node/server/warmup.ts b/packages/vite/src/node/server/warmup.ts
index 7911e0b647df07..9e1cf3ce043bb6 100644
--- a/packages/vite/src/node/server/warmup.ts
+++ b/packages/vite/src/node/server/warmup.ts
@@ -27,7 +27,7 @@ async function warmupFile(
   // transform html with the `transformIndexHtml` hook as Vite internals would
   // pre-transform the imported JS modules linked. this may cause `transformIndexHtml`
   // plugins to be executed twice, but that's probably fine.
-  if (file.endsWith('.html')) {
+  if (file.endsWith('.html') || file.endsWith('.htm')) {
     const url = htmlFileToUrl(file, server.config.root)
     if (url) {
       try {