The grey-faced sengi is endemic to the Udzungwa Mountains of south-central Tanzania. The sengi ranges from the forests of Ndundulu-Lauhomero to the Mwanihana forests. The Udzungwa Mountains are one part in a series of isolated mountain ranges stretching from southern Kenya to the south-central part of Tanzania. Due to the isolation of these mountains, a wide range of species developed, many of which cannot be found anywhere else. Only two populations are known, existing within an area covering around of forest. The natural habitat of this species falls within two nature reserves: The Udzungwa Ecological Monitoring Centre and the Udzungwa Mountains National Park. The habitat of the grey-faced sengi consists mostly of terrestrial system with moist, submontane and montane evergreen to upper montane closed-canopy forests, including bamboo thickets.