Flight DD7208 from Don Mueang to Surat Thani was scheduled to land at 7:20am but instead was diverted to Ranong airport while it waited for the fog to clear.
It landed at Surat Thani airport at 9am.
As a result, the return flight from Surat Thani to Don Mueang, flight DD7209, was delayed until 9.15am, rather than its scheduled take-off time of 7:50 am.
Other flights were not delayed, airport officials said.