Resource partitioning reduces resource competition between different species within the same habitat, promoting their coexistence. To understand how such species, co-adapt to reduce conflicts, we examined the behaviour of two primates, the Assamese macaque (Macaca assamensis) and the rhesus macaque (Macaca mulatta), from April 2017 to March 2018 in Sivapuri Nagarjun National Park (SNNP), Kathmandu Valley, Nepal. We performed 1,580 and 1,261 scan sessions on wild, multi-male/multi-female groups of Assamese and rhesus macaques, respectively, at 15-minute sampling intervals. Assamese macaques had a narrower food selection range than rhesus macaques, with 38 and 88 plant species consumed by Assamese and rhesus macaques, respectively. Overlapping food sources between the macaque species resulted in a Pianka index of 0.5. Assamese macaques consumed more items of tree, climber, and vine species, whereas rhesus macaques fed on more shrub, herb, and grass species. The proportions of plant parts consumed by Assamese and rhesus macaques also differed. Assamese macaques had a smaller home range (0.55 km2) than rhesus macaques (4.23 km2), and Assamese macaques moved more slowly (249.9 m/h) than rhesus macaques (959.6 m/h). Although feeding times did not differ between the two macaque species, less time was devoted to social activities by Assamese macaques (16.0%) than by rhesus macaques (33.7%). Assamese macaques were generally arboreal, with 94.0% of their activities conducted in trees, whereas rhesus macaques were largely terrestrial, with 58.5% of their activities conducted on the ground. These differences in food selection, home range size, ranging and activity patterns, and habitat use suggest that Assamese and rhesus macaques reduce resource competition through resource partitioning to coexist in the same habitat.