They have long, loose fur which is mainly blackish-brown, and a rufous tinged mane of longer hairs over the shoulders which is more noticeable in the males.

The bare skin on such places as the palms and soles is pink in newborns but darkens as the get older and is normally black by nine months of age.

[5] Osman Hill's mangabey occurs in low to medium altitude tropical rainforest where it is highly arboreal and can be seen in the canopy and emergent layers.

They have powerful jaws, hands and arms which makes it possible for them to extract seeds from harder fruits, e.g. those of Monodora myristica than similarly sized monkeys.

Important fruit tree species for Odsman Hill's mangabey include Erythrophleum suaveolens and Enantia chlorantha.

[5] Osman Hill's mangabey is a social subspecies living in groups of 10-20 individuals which consist of a few males, several females and their dependent young.