Police arrested three men and seized 250 kilograms of crystal meth, or "ice", in Phayao's Chiang Kham district late on Monday night.
Police acting on a tip-off spotted a 10-wheel truck and a pickup truck on the Chingkham-Joon road and followed the vehicles to a PTT petrol station in Tambon Chiangbal where they made the arrests.
The drugs were found in 13 bags on the 10-wheel truck.
Three suspects were arrested and identified as Montree Yodmaneebanphot, Sinchai Saelee and Banjong Saelee, all from Chiang Rai.
The suspects said they were hired by a drug boss in Myanmar to smuggle the drug to Ayutthaya to distribute to drug pushers in central provinces.
However, police suspect that Malaysia was the real destination where 1kg of ice can fetch Bt13.5 million on the street.
Police added that Montree was already wanted on an arrest warrant for allegedly smuggling 9.4 million meth pills and 788kgs of ice from Laos into Thailand earlier this month.