Kwanthai Sithmorseng has eight losses against eight opponents on his boxing record. For a list of Sithmorseng's best fights, refer to "Best fights of Kwanthai Sithmorseng".
On March 12, 2021 Kwanthai Sithmorseng faced off against Srisaket Sor Rungvisai at age 36. He was coming in with a record of 50-8-1 (27), and Rungvisai was 34 years old and with a record of 49-5-1 (42). Sithmorseng lost the fight via 3rd-round retirement.
On June 9, 2019 Kwanthai Sithmorseng faced off against Jayson Mama at age 34. He was coming in with a record of 49-7-1 (26). Sithmorseng lost the fight via 3rd-round TKO.
On May 5, 2018 Kwanthai Sithmorseng faced off against Wulan Tuolehazi at age 33. He was coming in with a record of 48-6-1 (26). Sithmorseng lost the fight via 4th-round TKO.
On December 3, 2017 Kwanthai Sithmorseng faced off against Masahiro Sakamoto in a flyweight bout at age 33. He was coming in with a record of 48-5-1 (26). Sithmorseng lost the fight via 3rd-round KO.
On May 6, 2015 Kwanthai Sithmorseng fought Ryoichi Taguchi in a light-flyweight world-title fight for Taguchi's WBA title. Sithmorseng was 30 years old and with a record of 47-4-1 (25), and Taguchi was 28 years old and with a record of 21-2-1 (8). Sithmorseng lost the fight via 8th-round TKO.
On August 8, 2014 Kwanthai Sithmorseng faced off against Stamp Kiatniwat in a flyweight bout at age 29. He was coming in with a record of 44-3-1 (23). Sithmorseng lost the fight via 12-round unanimous decision.
On September 11, 2013 Kwanthai Sithmorseng fought Kazuto Ioka in a light-flyweight world-title fight for Ioka's WBA title. Sithmorseng was 28 years old and with a record of 41-2-1 (21), and Ioka was 24 years old and with a record of 12-0 (8). Sithmorseng lost the fight via 7th-round KO.
On April 19, 2011 Kwanthai Sithmorseng met Muhammad Rachman in a strawweight (WBA) world-title defense fight. Sithmorseng was 26 years old and with a record of 29-1-1 (16). Sithmorseng lost the fight via 9th-round KO and lost the title.
