Police raided his house of Somporn Rampung, 25, after receiving information that it had been occupied by a group of drug addicts. When police arrived, they found Somporn, who grabbed a plastic bag inside the cottage and ran away.
He was later caught by police, who discovered the grenade was wrapped inside the bag.
Somporn admitted that he bought the grenade for B4,000 from another Thai man who he knows only as “Petch”.
He also admitted he has kept grenades before, usually swapping them for drugs. However his one seized yesterday he planned to use as a weapon, he told police.
M67 grenades are commonly used by the United States and Canadian militaries, and were common during the Vietnam War.
The grenades, when thrown, can kill within a radius of five metres, and injure people within a 15 metre radius. Fragments can disperse as far away as 250 metres.
In March, police received a report that a member of gang of drug dealers had thrown a grenade in Thalang, caused one injury.