The collared mangabey is native to tropical forests. It lives on the ground and lower layers of the forest in small groups of 4-12 individuals. It is a very social animal with a highly developed communication system. It actively communicates with other individuals through shrieks and facial gestures. The collared mangabey is sure-footed, moving easily among the tree branches. Its tail is partly prehensile allowing it to keep ahold of branches. The leopard is its primary threat.

Their diet consists of palm nuts, seeds, fruit and leaves.

Their body is powerful although slender. It has very long legs and a relatively short, stiff tail which is held up over its back. Its coat is grey with a white underside. The head of mangabey is reddish brown. The length of head and body is 65 cm, tail 70 cm and the weight is up to 12 kg.

Breeding takes place at any time of year, with a single youngster being born after about 6 months, fully furred and with its eyes open. The mother gives birth wherever she happens to be, and birth is usually at night. She eats the placenta and licks the baby clean as it clings to her belly. Other females in the group show great interest and try to hold new infants. Nursing becomes less frequent after the first few months, but continues until the next birth, usually after 2 years.

They are found from W Nigeria to Gabon.