The average group size is around 40 individuals. These large groups are divided into sub-groups of 2 – 6 individuals who together forage for food. The groups sleeping sites are usually located near water, the sleeping sites become regular spots and repeatedly used. The Allens swamp monkey has a multimale-multifemale social system.

Allen’s Swamp monkey makes a grunting sound that is used to maintain contact between members of the group. Individuals will groom each other to remove dead skin and parasites. This kind of behaviour reinforces bonds between two individuals.

The Allen’s Swamp monkey inhabits swampy, water-rich areas. They are very good swimmers and can dive well. When threatened, they can quickly dive into the waters to avoid danger.

Allen’s Swamp Monkey is a diurnal animal (active during the day and sleeping at night) and regularly looks for food on the ground. Allen’s Swamp Monkeys diet consists of fruits and leaves as well as beetles and worms and other small invertebrates. Allen’s Swamp Monkeys lifespan can be as long as 23 years.