Conserving the world's biodiversity is one of today's strategic challenges for sustainable development. Primates are increasingly threatened by habitat destruction, climate change and poaching. The aim of this article is therefore to study their behaviour in the wild as well as the ecological factors that influence this behaviour on the periphery of the Dja Biosphere Reserve, with the aim of improving their conservation. To do this, direct methods based on the counting of primates observed during reconnaissance walks along the transects and outside the transects in various vegetation facies (old secondary forest, young forest, riparian forest, swamp forest and forest gaps) made it possible to count 826 individuals divided into 6 species. The species Cercopithecus pogonias is the most abundant with 373 individuals, i.e. 45.16%, followed by Cercopithecus cephus cephus (228 individuals), representing 27.60% and finally Cercocebus agilis (133 individuals), i.e. 16.10%. The species with the lowest representation are Pan troglodytes (1.45%) and Lophocebus albigena (2.91%). This population of primates is made up mainly of adults (365 individuals) and juveniles (256 individuals). These primates are essentially frugivorous, which is why they are concentrated in the sectors where certain tree species are found, such as Upaca sp. which account for 30.60% of the primate population, followed by Irvingia gabonensis (8%), then Landolphia sp. (7.26%) and finally Terminalia superba (6.42%). Most primates in the periphery of the Dja reserve (35.42%) feed in the morning before noon, while only 14.58% do so in the afternoon. The majority of these primates also wander around in the morning (27.08%) more than in the afternoon (12.05%), certainly in search of food. These primates are found in young (62.11%) and old (27.97%) secondary forests. Very few frequent or inhabit raphias, riparian forests or forest gaps. However, there is a significant difference between the number of individuals in mature secondary forests and young secondary forests. Understanding the behavioural ecology of these primates is therefore important to improve their conservation.