Cognomen Mstislavskiy (Mstislavskiy 
, Мстиславский 
) , all over the world, is a rare surname. The cognomen Mstislavskiy is habitual in Russia, where it is a rare surname, Belarus, where it is a very rare surname, and the United States, where it is an extremely rare surname.
| VARIANT | COUNTRY |
|---|---|
| Mstislavskiy | United States |
| Мстиславский | Russia, Belarus |