Mastuj () is a tehsil and a valley in Upper Chitral District in Khyber Pakhtunkhwa province of Pakistan. Mastuj is the principal settlement. It is located at 36ð17'0N 72ð31'0E with an altitude of 2359 metres (7742 feet). There are ruins of old fort built originally in 18th century and reconstructed several times.
The main villages include Buni, Charun-Oweer, Mastuj, Khouzh, Kargin, Marthing, Chuinj, Parkusap, Reshun, Parwak, Kuragh, Aveer, Chapali and Brep.
Tehsil Mastuj starts right after the end of Baranis, Reshun, Kuragh, Buni, Aveer, Parwak, Mastuj, Chinar, Chuinj, Chapali, Brep, Bang and Meragram are the main areas of Tehsil Mastuj.