The Sanje mangabey (Cercocebus sanjei) is a highly endangered Old World monkey of the white-eyelid mangabey group from Tanzania. They are about 50–65 centimeters long, excluding tail, and weigh about 7–9 kilograms, and their body color is greyish. They live in valley forests, but are mostly ground-dwelling, which makes them susceptible to hunting and poaching. Fruit makes up about 70% of their diet, while foliage makes up most of the rest.