The tour bus was heading to Mae Sot district in western Thailand bordering Myanmar when it collided head on with an 18 wheeler carrying a full load of sugar in Kamphaeng phet province.
The bus was carrying 48 passengers. Both drivers died on the spot, police said.
It was not immediately known if any foreigner was in the tour bus. Three passengers in the bus died and one in the truck was also killed.
Another25 injured passengers were taken to Khong Khlung hospital.