The blast occurred when 10 soldiers were travelling in a truck in Krong Pinang district.
Police said suspected insurgents hiding in nearby plantations detonated the bomb buried in the road as the military vehicle passed by.
Eight soldiers were killed instantly and two others wounded. Two civilians riding on a motorcycle were also injured, Nation newspaper said.
There have been near daily assaults on security forces and civilians despite peace talks on June 14 in which the Thai government and the Barisan Revolusi Nasional (BRN) agreed to work toward curbing violence over Ramadan.
The decade long insurgency in Buddhist majority Thailand's three southern provinces has claimed more than 5,000 lives in sporadic attacks.