Mae Hong Son Province is approximately 924 kilometres (574 mi) north of Thailand's capital city Bangkok. To the north and west it connects to a total of three states in the Union of Burma, namely the southern portion of Shan State, Kayah State, and Kawthoolei State, via the West Thanon Thongchai Mountains, and the rivers Salween and Moei. These formations serve as natural boundaries between the countries. To the south, it connects to the district of Tha Song Yang and Tak, via the rivers Yuam and Ngao, which serve as a provincial boundary. To the east it connects to the districts of Wiang Haeng, Chiang Dao, Mae Taeng, Mae Chaem, Hot and Omkoi in Chiang Mai Province, via the Central and East sections of the Thanon Thongchai mountain ranges, which serve as a boundary between the two provinces.
Every district in Mae Hong Son Province shares a common border, measuring approximately 483 kilometres in total length, with the Union of Burma. The common border consists of approximately 326 km (203 mi) of land boundary and 157 km (98 mi) of river boundary (not counting the Salween, 127 km (79 mi), and Moei, 30 km (19 mi)).