A man serving a sentence on drug charges was found hanged in his sleeping quarters at a prison in Tak's Mae Sot district on Monday morning, police said.
Pol Capt Chairat Nankas, the duty officer at Mae Sot police station, said police, doctors and administrative officials went to the prison to investigate after the man's death was reported.
He was identified as Don Phaptip, 35, who was sentenced by the Mae Sot Court on June 19 to nine years in jail after being found guilty of having drugs in his possession with intent to sell.
He was believed to have hanged himself.
His body was sent to Mae Sot Hospital for autopsy.