The Sanje mangabey is endemic to Tanzania's Udzungwa Mountains. The 2024 conservation plan reports it from two separated forest fragments.
Its coat is speckled gray with a pale-orange underside. Long crown hairs sweep up and back, and the face is pale gray with pink around the eyes and nose.
In Udzungwa forest, it often uses the lower understory and forages on the forest floor. Observations summarized in EAZA guidance report fruit as the main diet, with fungi and seeds also eaten.
An extinction-risk assessment has not been added yet.