The driver, who was injured in the accident, lost control of the vehicle before it fell about 30m into the ravine on a curvy rural road in Wang Nuea district on Wednesday, police Colonel Somdet Tossaporn said.
The travellers were coming from the temple after making merit – a Buddhist ritual of performing good deeds or other acts. Most of those killed were women.
Up to 26,000 people are killed in road accidents every year in Thailand, according to the Interior Ministry.
A recent report by the World Health Organisation said the country saw about 38.1 road deaths per 100,000 of population, compared to an average of 18.5 in Southeast Asia as a whole.