The Kayah-Karen montane rain forests occupy an area of 119,158 km². The mountain ranges lie in the border region between Myanmar and Thailand. The Dawna, Thanon Thong Chai, Daen Lao, and Khun Tan ranges separate the Salween River basin to the west from that of the Chao Phraya and Mekong rivers on the east. The Karen Hills extend to the northwest, separating the Salween and Sittaung River basins. The ecoregion includes the valley of the Salween River in Kayin, Kayah, and southern Shan states.