The men, aged between 22 and 45, succumbed to smoke inhalation in the blaze, said Police Colonel Supakorn Piwon, commander of the police station in Sai Noi about 20 kilometres northwest of the capital.
The fire was caused by an electrical fault, he told AFP, adding that the victims were all suspects being held in cells at the police station.
"We tried but could not get inside to help them. The electricity was off and there was a lot of fire and smoke so we could not go in," he said.