The Darkhad valley is a large valley in northwestern Khövsgöl aimag, Mongolia. It is situated between the Ulaan Taiga and Khoridol Saridag ranges at an altitude of about 1600 m, about 160 km long and 40 km wide. The area is 4270 km². It was transferred from the People's Republic of Tannu Tuva to the Mongolian People's Republic in 1925 as a Soviet concession to the Mongolians, who had wanted to incorporate the territory of Tannu Uriankhai into their country.