diff --git a/src/index.ts b/src/index.ts
index 4f3c29d..641e9f1 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,5 +1,6 @@
 import {
   isRef,
+  triggerRef,
   computed as vueComputed,
   customRef as vueCustomRef,
   readonly as vueReadonly,
@@ -40,12 +41,18 @@ function toFunctional(raw: any, readonly: boolean): any {
     ])
   )
 
+  const set = (value: any) => (raw.value = value)
+  const mutate = (mutator: (value: any) => any) => {
+    mutator(raw.value)
+    triggerRef(raw)
+  }
+
   return new Proxy(fn, {
     ...handlers,
     get(target, key) {
-      if (!readonly && key === 'set') {
-        return (value: any) => (raw.value = value)
-      } else if (key === '__raw_ref') {
+      if (!readonly && key === 'set') return set
+      else if (!readonly && key === 'mutate') return mutate
+      else if (key === '__raw_ref') {
         return toRawRef(raw)
       } else {
         return Reflect.get(raw, key, raw)
diff --git a/tests/index.test.ts b/tests/index.test.ts
index 3976d44..eef27ce 100644
--- a/tests/index.test.ts
+++ b/tests/index.test.ts
@@ -5,6 +5,7 @@ import {
   customRef,
   isReadonly,
   isRef,
+  nextTick,
   reactive,
   readonly,
   ref,
@@ -234,3 +235,24 @@ test('export types', () => {
     keyof typeof vueReactivityType
   >()
 })
+
+test('mutate', async () => {
+  const fn = vi.fn()
+
+  const foo = ref({ foo: 'foo', nested: { count: 1 } })
+  watch(
+    () => foo().nested.count,
+    () => fn()
+  )
+
+  foo.mutate((foo) => {
+    foo.foo = 'bar'
+    foo.nested.count++
+  })
+
+  await nextTick()
+
+  expect(foo().foo).toBe('bar')
+  expect(foo().nested.count).toBe(2)
+  expect(fn).toBeCalledTimes(1)
+})
diff --git a/types.d.ts b/types.d.ts
index 3c13537..b8bf4ca 100644
--- a/types.d.ts
+++ b/types.d.ts
@@ -69,7 +69,12 @@ export declare type FunctionalRef<
   Writable extends boolean = boolean
 > = {
   (): T
-} & (Writable extends true ? { set: (value: T) => void } : {})
+} & (Writable extends true
+  ? {
+      set: (value: T) => void
+      mutate: (mutator: (value: T) => void) => void
+    }
+  : {})
 
 export declare interface ComputedRef<T = any> extends WritableComputedRef<T> {
   set: never