diff --git a/packages/misskey-js/src/acct.ts b/packages/misskey-js/src/acct.ts
index aa8658cdbd..469cc35b14 100644
--- a/packages/misskey-js/src/acct.ts
+++ b/packages/misskey-js/src/acct.ts
@@ -6,6 +6,7 @@ export type Acct = {
 export function parse(_acct: string): Acct {
 	let acct = _acct;
 	if (acct.startsWith('@')) acct = acct.substring(1);
+	else if (acct.startsWith('acct:')) acct = acct.substring(5);
 	const split = acct.split('@', 2);
 	return { username: split[0], host: split[1] || null };
 }
diff --git a/packages/misskey-js/test/acct.ts b/packages/misskey-js/test/acct.ts
new file mode 100644
index 0000000000..6db8aea58b
--- /dev/null
+++ b/packages/misskey-js/test/acct.ts
@@ -0,0 +1,35 @@
+import { describe, it, expect } from 'vitest';
+import * as acct from '../src/acct.js';
+
+describe('acct.parse', () => {
+	it('parses plain username', () => {
+		const res = acct.parse('alice');
+		expect(res).toEqual({ username: 'alice', host: null });
+	});
+
+	it('parses at-mark style without host', () => {
+		const res = acct.parse('@alice');
+		expect(res).toEqual({ username: 'alice', host: null });
+	});
+
+	it('parses at-mark style with host', () => {
+		const res = acct.parse('@alice@example.com');
+		expect(res).toEqual({ username: 'alice', host: 'example.com' });
+	});
+
+	it('parses acct: style', () => {
+		const res = acct.parse('acct:alice@example.com');
+		expect(res).toEqual({ username: 'alice', host: 'example.com' });
+	});
+});
+
+describe('acct.toString', () => {
+	it('returns username when host is null', () => {
+		expect(acct.toString({ username: 'alice', host: null })).toBe('alice');
+	});
+
+	it('returns username@host when host exists', () => {
+		expect(acct.toString({ username: 'alice', host: 'example.com' })).toBe('alice@example.com');
+	});
+});
+