Cognomen Onsai (Onsai 
) , globally, is a very rare surname. The last name Onsai is habitual in Thailand, where it is a very rare surname, Malaysia, where it is an extremely rare surname, and China. Much less frequently, Onsai is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Onsai | India, China, Malaysia, Thailand |