Acting on a tip-off, soldiers and police raided a shelter in Moo 1 village in Tambon Ban Khuan in Muang Satun district at 3am on Tuesday and found 5kg of marijuana in a Toyota pick-up truck.
Winai Lenphet, 22, and Wirat Hadnern, 36, were arrested at the scene.
The two suspects implicated Rokard Hadnern, 55, who was arrested at his house in Thapae district later in the day. Authorities found 200kg of marijuana at the house.
Police said the men admitted that they had bought the drugs in Nong Khai for Bt5,000 per kilogram and they were planning to smuggle it to Malaysia where each kilogram would fetch Bt50,000.