diff --git a/__tests__/unit/node/config.test.ts b/__tests__/unit/node/config.test.ts
new file mode 100644
index 000000000..9837879c3
--- /dev/null
+++ b/__tests__/unit/node/config.test.ts
@@ -0,0 +1,39 @@
+import { mergeConfig } from 'node/config'
+import type { MarkdownItAsync } from 'markdown-it-async'
+
+describe('node/config', () => {
+  test('merges markdown config hooks from extended configs', async () => {
+    const calls: string[] = []
+    const md = {} as MarkdownItAsync
+
+    const merged = mergeConfig(
+      {
+        markdown: {
+          lineNumbers: true,
+          config() {
+            calls.push('base')
+          }
+        }
+      },
+      {
+        markdown: {
+          attrs: {
+            allowedAttributes: ['id']
+          },
+          async config() {
+            calls.push('extended')
+          }
+        }
+      }
+    )
+
+    expect(merged.markdown?.lineNumbers).toBe(true)
+    expect(merged.markdown?.attrs).toEqual({
+      allowedAttributes: ['id']
+    })
+
+    await merged.markdown?.config?.(md)
+
+    expect(calls).toEqual(['base', 'extended'])
+  })
+})
diff --git a/src/node/config.ts b/src/node/config.ts
index bdcd00e17..26bf6c0ee 100644
--- a/src/node/config.ts
+++ b/src/node/config.ts
@@ -7,7 +7,8 @@ import {
   loadConfigFromFile,
   mergeConfig as mergeViteConfig,
   normalizePath,
-  type ConfigEnv
+  type ConfigEnv,
+  type UserConfig as ViteUserConfig
 } from 'vite'
 import { DEFAULT_THEME_PATH } from './alias'
 import type { DefaultTheme } from './defaultTheme'
@@ -22,6 +23,7 @@ import {
   type HeadConfig,
   type SiteData
 } from './shared'
+import type { MarkdownOptions } from './markdown/markdown'
 import type { RawConfigExports, SiteConfig, UserConfig } from './siteConfig'
 import { glob } from './utils/glob'
 
@@ -288,10 +290,14 @@ async function resolveConfigExtends(
   return resolved
 }
 
-export function mergeConfig(a: UserConfig, b: UserConfig, isRoot = true) {
+export function mergeConfig<A extends object, B extends object>(
+  a: A,
+  b: B,
+  isRoot = true
+): A & B {
   const merged: Record<string, any> = { ...a }
   for (const key in b) {
-    const value = b[key as keyof UserConfig]
+    const value = b[key]
     if (value == null) {
       continue
     }
@@ -302,7 +308,12 @@ export function mergeConfig(a: UserConfig, b: UserConfig, isRoot = true) {
     }
     if (isObject(existing) && isObject(value)) {
       if (isRoot && key === 'vite') {
-        merged[key] = mergeViteConfig(existing, value)
+        merged[key] = mergeViteConfig(
+          existing as ViteUserConfig,
+          value as ViteUserConfig
+        )
+      } else if (isRoot && key === 'markdown') {
+        merged[key] = mergeMarkdownConfig(existing, value as MarkdownOptions)
       } else {
         merged[key] = mergeConfig(existing, value, false)
       }
@@ -310,6 +321,19 @@ export function mergeConfig(a: UserConfig, b: UserConfig, isRoot = true) {
     }
     merged[key] = value
   }
+  return merged as A & B
+}
+
+function mergeMarkdownConfig(a: MarkdownOptions, b: MarkdownOptions) {
+  const merged = mergeConfig(a, b, false)
+  const baseConfig = a.config
+  const extendedConfig = b.config
+  if (baseConfig && extendedConfig) {
+    merged.config = async (md) => {
+      await baseConfig(md)
+      await extendedConfig(md)
+    }
+  }
   return merged
 }