Predator–prey dynamics are an important aspect of community ecology, but predation events are often difficult to observe. Among African primates, observations of mammal predation are particularly uncommon and generally restricted to a few ape and cercopithecoid species. I report five observations of mammal predation by golden-bellied mangabeys (Cercocebus chrysogaster) living in rainforest at the LuiKotale study site, Democratic Republic of the Congo. Over 46 all-day follows, mangabeys from one group caught and consumed four duikers (Cephalophinae spp.) and one Alexander’s cusimanse (Crossarchus alexandri). Individuals begged from the feeding individual in three of five observations. I observed one successful attempt at begging, which resulted in an adult female tolerating removal of blue duiker by a juvenile. These are the first detailed observations of mammal predation and food sharing by Cercocebus mangabeys and suggest mammals that feed alongside mangabeys may balance predation risk against social foraging benefits. Food sharing is rarely observed in most cercopithecine monkeys and could provide a useful metric to examine socio-ecological patterns of food acquisition.