Police said that the bus driver, 51-year old Nirun Faramee, escaped unscratched and is being held in police custody for interrogation.
The accident occurred at a spot about 16 kilometres from That Phanom district on highway No 212 between That Phanom and Muk Dahan.
It was reported that the mini bus was heading for Nakhon Phanom with 12 passengers on board.
Upon approaching the scene of the accident which was a curve, the bus skidded out of the road which was slippery at the time from rains, ploughed into a tree before turning one side up and continued sliding until it rammed into the second tree.
Two passengers were thrown out of the vehicle by the force of the impact and killed. The rest of the passengers were injured with two of them seriously injured. They were eventually rushed to Somdet Yupparaj hospital in That Phanom district by rescue workers.
The driver claimed that he drove the vehicle at only 90 kilometres per hour and blamed the slippery road for the accident. However, police said they would question him further.
Mr Yodpetch Kamsaengdee, the provincial highway official, said motorists had been warned regularly to drive with caution on the road in question because it is narrow and without road shoulders but often busy.