Police on Saturday arrested three Hmong tribesmen and seized drugs with an estimated street value of more than 450 million baht at Chatuchak market.
The haul included 1.45 million methamphetamine pills and eight kilogrammes of crystal methamphetamine, said officers.
Police said they had received intelligence reports that the three men had rented a stall at Chatuchak market, ostensibly to sell Hmong bags and handicrafts.
Officers staked out the area, believing the drugs were on the scene.
About 5am Saturday, the three suspects came to the stall. While one of them was opening a locker, police arrested the three. When officers searched the stall's back room they found the "ya ba" pills and the "ya ice".
Charged with possessing illegal drugs for sale were Kasama Charoenman, 37, Anuchon Laojang, 20, and Panya Wangtrakul, 25.
Police said the suspects admitted they had been paid 380,000 baht by a Hmong drug ring in a northern border province to transport the illicit drugs to Bangkok.