Assamese macaques (Macaca assamensis) and rhesus macaques (M. mulatta) are sympatrically distributed in Nepal but differ in many traits. Data on 11 groups of Assamese macaques and 13 groups of rhesus macaques in northwestern Kathmandu show that Assamese macaques inhabited only protected forests in Shivapuri Nagarjun National Park, whereas rhesus macaques inhabited even small forests disturbed by people in temples close to cultivated and urban areas, frequently raided crops, and were provisioned. Assamese macaques inhabited higher altitude and formed smaller groups with more adult males and fewer immatures than rhesus macaques. Rhesus macaques' proclivity to be provisioned supported their large groups. However, their strict dominance hierarchy might make low-ranking males solitary, whereas many males of Assamese macaques might be able to stay together because of their affiliative relationship with other males. In Nepal, Assamese macaques might adopt more K-reproductive strategies with a larger body, fewer offspring, and lower twin frequency in stable circumstances, compared to rhesus macaques. Competition for resources promotes niche separation in food choice and habitat use, which might strengthen the inter-species difference and make their coexistence possible. We recommend careful maintenance of forests to protect Assamese macaques, and effective managements of provisioned and crop-raiding rhesus macaques.