Supachai Koysub is an athlete and Paralympian from Thailand competing mainly in category T54 sprint events.
He competed in the 2000 Summer Paralympics in Sydney, Australia. There he won a gold medal in the men's 200 metres - T54 event, a gold medal in the men's 4 x 100 metre relay - T54 event, a silver medal in the men's 4 x 400 metre relay - T54 event, finished fourth in the men's 100 metres - T54 event and went out in the semi-finals of the men's 800 metres - T54 event. He also competed at the 2004 Summer Paralympics in Athens, Greece. There he won a gold medal in the men's 4 x 100 metre relay - T53-54 event, a gold medal in the men's 4 x 400 metre relay - T53-54 event, was disqualifed in the men's 100 metres - T54 event, finished fourth in the men's 200 metres - T54 event and finished seventh in the men's 400 metres - T54 event. He also competed at the 2008 Summer Paralympics in Beijing, China. There he won a silver medal in the men's 4 x 100 metre relay - T53-54 event, a silver medal in the men's 4 x 400 metre relay - T53-54 event, a bronze medal in the men's 100 metres - T54 event, went out in the first round of the men's 200 metres - T54 event and finished sixth in the men's 400 metres - T54 event