Four men who died at scene were all privates, identified as Adisak Aoraek, Pakin Phoskin, Natthawut Somwong and Preecha Tohteh.
Five soldiers were hospitalised in critical condition, while another five suffered minor injuries.
A fifth death was added to the toll when Pvt Jakkrit Ubonchinda was pronounced dead at hospital.
The incident took place at noon when an army truck belonging to Pattani Special Task Force 25 was carrying 12 soldiers to change shift with another group at Ingkhayuthboriharn army camp.
A 50kg homemade bomb planted beneath the road surface was detonated as the truck passed Baan Magor Village in Kapho district. The bombing scene was only 100 metres from Baan Magor School
Security personnel are now seeking suspected insurgents thought to be involved with the attack.