Mae Sariang District (Thai: แม่สะเรียง, pronounced [mɛ̂ː sā.rīa̯ŋ]) is a small town and district (amphoe) on the narrow valley along Yuam River in Mae Hong Son Province, northern Thailand, along the Myanmar border. The areas around Mae Sariang are mountainous and forested; flat terrain that suits population or agriculture is scarce. The local population of Mae Sariang is of mixed origin. The main ethnicity in the low land plain, town center and its satellite villages along the river is Tai Yuan (Northern Thai or Lanna people) with some cross-marriage with other ethnicities. There are also Tai Yai or Shan people in the town center; they are among the first groups that inhabited the area. Red Karen and Karen descendants also reside in the town with a high density in the Christian quarter of the town. There is a sizable Bengali Muslim community and a mosque near the central market. The area has many links to Burma, such as its architecture and a large population of Burmese Muslims. Mae Sariang represents the westernmost area where Lanna culture and architecture dominated which also well assimilated with Burmese/ Shan.
Neighboring districts are (from north clockwise): Mae La Noi of Mae Hong Son Province; Mae Chaem and Hot of Chiang Mai Province; Sop Moei of Mae Hong Son Province; and Kayin State and Kayah State of Myanmar.