Surname อุสิทธิ์ (อุสิทธิ์ 
) , throughout the world, is a very rare last name. The family name อุสิทธิ์ is characteristic of South-eastern Asia, particularly Thailand, where it is a very rare surname. Much less frequently, อุสิทธิ์ is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| อุสิทธิ์ | Thailand |