Estimation of population size is a core of wildlife population ecology and conservation. Although GPS collars has long been considered as an effective and promising method on monitoring behavior of wildlife, few studies have used this technique to estimate wildlife population size. In this study, we used the GPS telemetry method for conducting population census. We deployed GPS collars on 32 rhesus macaques (Macaca mulatta) in 9 groups on a small island and collected 109,739 fixes from May 2021 to April 2022. We used fixes of all tracked individuals within a group to calculate home range for each group. The annual home range of 9 groups ranged from 13.9 ha to 55.4 ha. Home ranges had substantial overlap with neighboring groups, and the largest ratio of exclusively use occurred in March. We estimated that the study area had the capacity to accommodate 38.6 macaque groups within their respective home ranges and the population size was 957 ± 193 macaques on the island by multiplying the mean group size (24.8 ± 5.0). In addition, we compared the similarity of utilization distribution between each individual and their belonging group. The result indicated that using a single individual’s dataset could represent the whole group’s home range and utilization pattern on most occasions. Our method is labor saving, independent of experience and observational ability of surveyors, of high repeatability, and can generate a huge amount of fixes to explore other important ecological questions.