diff --git a/benchmarks/typed/isWeakSet.bench.ts b/benchmarks/typed/isWeakSet.bench.ts
new file mode 100644
index 00000000..7a32c8d5
--- /dev/null
+++ b/benchmarks/typed/isWeakSet.bench.ts
@@ -0,0 +1,9 @@
+import * as _ from 'radashi'
+import { bench } from 'vitest'
+
+describe('isWeakSet', () => {
+  bench('with no arguments', () => {
+    _.isWeakSet()
+  })
+})
+
diff --git a/docs/typed/isWeakSet.mdx b/docs/typed/isWeakSet.mdx
new file mode 100644
index 00000000..9ca3089d
--- /dev/null
+++ b/docs/typed/isWeakSet.mdx
@@ -0,0 +1,16 @@
+---
+title: isWeakSet
+description: Returns true for WeakSet instances
+---
+
+## Basic usage
+
+Returns true for `WeakSet` instances, even if they are subclass instances or from
+other [realms](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/instanceof#instanceof_and_multiple_realms).
+
+```ts
+import * as _ from 'radashi'
+
+_.isWeakSet(new WeakSet()) // true
+_.isWeakSet(new (class extends WeakSet {})()) // true
+```
diff --git a/src/mod.ts b/src/mod.ts
index 1307a1dc..b2d87fd7 100644
--- a/src/mod.ts
+++ b/src/mod.ts
@@ -114,5 +114,6 @@ export * from './typed/isSet.ts'
 export * from './typed/isString.ts'
 export * from './typed/isSymbol.ts'
 export * from './typed/isTagged.ts'
+export * from './typed/isWeakSet.ts'
 
 export * from './types'
diff --git a/src/typed/isWeakSet.ts b/src/typed/isWeakSet.ts
new file mode 100644
index 00000000..a8e8034a
--- /dev/null
+++ b/src/typed/isWeakSet.ts
@@ -0,0 +1,7 @@
+import { isTagged } from 'radashi'
+
+export function isWeakSet<T extends WeakKey = WeakKey>(
+  value: unknown,
+): value is WeakSet<T> {
+  return isTagged(value, '[object WeakSet]')
+}
diff --git a/tests/typed/isWeakSet.test.ts b/tests/typed/isWeakSet.test.ts
new file mode 100644
index 00000000..45ead106
--- /dev/null
+++ b/tests/typed/isWeakSet.test.ts
@@ -0,0 +1,23 @@
+import * as vm from 'node:vm'
+import * as _ from 'radashi'
+
+describe('isWeakSet', () => {
+  test('returns true for WeakSet instances', () => {
+    expect(_.isWeakSet(new WeakSet())).toBe(true)
+  })
+  test('returns true for WeakSet subclass instances', () => {
+    expect(_.isWeakSet(new (class extends WeakSet {})())).toBe(true)
+  })
+  test('returns true for WeakSet instances from other realms', () => {
+    expect(_.isWeakSet(vm.runInNewContext('new WeakSet()'))).toBe(true)
+  })
+  test('returns false for undefined', () => {
+    expect(_.isWeakSet(undefined)).toBe(false)
+  })
+  test('returns false for null', () => {
+    expect(_.isWeakSet(null)).toBe(false)
+  })
+  test('returns false for non-WeakSet objects', () => {
+    expect(_.isWeakSet({})).toBe(false)
+  })
+})