diff --git a/src/index.ts b/src/index.ts
index a44702e..68fdb26 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -16,6 +16,7 @@ import { FSWatcher } from 'chokidar'
 import glob from 'globby'
 import { PrettyError } from './errors'
 import { postcssPlugin } from './plugins/postcss'
+import { externalPlugin } from './plugins/external'
 
 const textDecoder = new TextDecoder('utf-8')
 
@@ -58,7 +59,7 @@ export type Options = {
       }
   sourcemap?: boolean
   /** Don't bundle these packages */
-  external?: string[]
+  external?: (string | RegExp)[]
   /** Transform the result with `@babel/core` */
   babel?: boolean
   /**
@@ -136,7 +137,12 @@ export async function runEsbuild(
         jsxFragment: options.jsxFragment,
         sourcemap: options.sourcemap,
         target: options.target === 'es5' ? 'es2016' : options.target,
-        plugins: [postcssPlugin],
+        plugins: [
+          // esbuild's `external` option doesn't support RegExp
+          // So here we use a custom plugin to implement it
+          externalPlugin(external),
+          postcssPlugin,
+        ],
         define: {
           ...options.define,
           ...Object.keys(env).reduce((res, key) => {
@@ -146,7 +152,6 @@ export async function runEsbuild(
             }
           }, {}),
         },
-        external,
         outdir:
           options.legacyOutput && format !== 'cjs'
             ? join(outDir, format)
diff --git a/src/plugins/external.ts b/src/plugins/external.ts
new file mode 100644
index 0000000..2bb2375
--- /dev/null
+++ b/src/plugins/external.ts
@@ -0,0 +1,25 @@
+import { Plugin } from 'esbuild'
+
+export const externalPlugin = (patterns?: (string | RegExp)[]): Plugin => {
+  return {
+    name: `external`,
+
+    setup(build) {
+      if (!patterns || patterns.length === 0) return
+
+      build.onResolve({ filter: /.*/ }, (args) => {
+        const external = patterns.some((p) => {
+          if (p instanceof RegExp) {
+            return p.test(args.path)
+          }
+          return args.path === p
+        })
+        if (external) {
+          return { path: args.path, external }
+        }
+        // return without `path` to use default path resolution logic
+        return {}
+      })
+    },
+  }
+}
diff --git a/test/index.test.ts b/test/index.test.ts
index 812b6c2..558792f 100644
--- a/test/index.test.ts
+++ b/test/index.test.ts
@@ -363,3 +363,37 @@ test('import css', async () => {
     ]
   `)
 })
+
+test('external', async () => {
+  const { output } = await run(getTestName(), {
+    'input.ts': `export {foo} from 'foo'
+    export {bar} from 'bar'
+    export {baz} from 'baz'
+    `,
+    'node_modules/foo/index.ts': `export const foo = 'foo'`,
+    'node_modules/foo/package.json': `{"name":"foo","version":"0.0.0"}`,
+    'node_modules/bar/index.ts': `export const bar = 'bar'`,
+    'node_modules/bar/package.json': `{"name":"bar","version":"0.0.0"}`,
+    'node_modules/baz/index.ts': `export const baz = 'baz'`,
+    'node_modules/baz/package.json': `{"name":"baz","version":"0.0.0"}`,
+    'tsup.config.ts': `
+    export default {
+      external: [/f/, 'bar']
+    }
+    `,
+  })
+  expect(output).toMatchInlineSnapshot(`
+    "\\"use strict\\";Object.defineProperty(exports, \\"__esModule\\", {value: true});// input.ts
+    var _foo = require('foo');
+    var _bar = require('bar');
+
+    // node_modules/baz/index.ts
+    var baz = \\"baz\\";
+
+
+
+
+    exports.bar = _bar.bar; exports.baz = baz; exports.foo = _foo.foo;
+    "
+  `)
+})