The Cardamom mountain range forms the boundary to Cambodia in the east of the province, where Trat has borders with three Cambodian provinces: Battambang, Pursat and Koh Kong. The third biggest island of Thailand is Ko Chang, belonging to the province. The island, together with more than 40 surrounding smaller islands, forms the Mu Ko Chang Marine National Park.
Koh Chang is Thailand's second-largest island, located in Trat province.