| Thongchai Ratchai | |
| Fullname: | Thongchai Ratchai |
| Birth Date: | 31 October 1982 |
| Birth Place: | Roi Et, Thailand |
| Position: | Forward |
| Years1: | 2007 |
| Clubs1: | Suphanburi |
| Years2: | 2008 |
| Years3: | 2009 |
| Clubs3: | Suphanburi |
| Years4: | 2010 |
| Clubs4: | Sriracha |
| Years5: | 2011–2014 |
| Years6: | 2015–2017 |
| Years7: | 2017 |
| Clubs7: | Rayong |
Thongchai Ratchai (Thai: ธงไชย รัฐไชย, born October 31, 1982), nicknamed Thong (Thai: ธง), is a retired professional footballer who played as a forward from Roi Et Province, Thailand.