Mammalian species are key in maintaining a healthy ecosystem. The tropical rainforest in Borneo is characterized by its rich biodiversity and rugged interior, which houses various forest types from the lowland dipterocarps forest to the montane and ericaceous forests above 1,500 m. Using the data obtained from 81 camera trap stations set up from April 2023 to September 2024, we investigated the diversity of mammalian species across the spatial and temporal dimensions. We detected 35 species of mammals, from 6 orders and 15 families. We reported a bimodal peak for the average number of species per station, at 800-899 m and 1700-1799 m. The pig-tailed macaque Macaca nemestrina is the most abundant species in the study site, followed by the red muntjacs Muntiacus muntjak. Temporally, all the individual species’ activity patterns followed the previous studies, except for the mousedeer Tragulus spp., which is predominantly nocturnal. While other studies in Borneo observed more diurnality in mousedeer, we think the difference may be a co-existence strategy to reduce predation risk. We also reported evidence of spatial partitioning between the two species of muntjacs based on elevation. In conclusion, our results offer baseline knowledge on the spatial and temporal distribution pattern of non-volant mammals in a high-altitude protected area.