Microplastic pollution is a global concern arising from the extensive production and use of plastics. The prevalence of microplastics (MPs) in the environment is escalating due in large part to the excessive use of plastics in various human-related activities. Consequently, animals are being exposed to MPs through dietary intake, which poses significant health risks to the wild populations. The objective of the study was to assess the concentration of MPs in the feces of wild long-tailed macaques () in the Kosumpee Forest Park (KFP) located in Northeast Thailand. KFP is situated in close proximity to the town of Kosum Phisai and experiences considerable human-primate interaction. Fresh fecal drops from 50 adult macaques were collected and sampled. MP presence in the feces was measured using density separation through visual identification under a stereomicroscope. We found a total of 396 MP particles in the feces with an average of 7.9 particles/macaque. Two forms of MPs were found in the macaques' feces including fibers (391 pieces; 98.73%) and asymmetric fragments (5 pieces; 1.27%), with sizes mostly ranging under 1000 µm. The most observed color of MPs was blue (152 pieces; 38.48%). This study highlights the impact of anthropogenic waste and the potential health problems that can be caused to wild animals via microplastic pollution. The results contribute to the ongoing discussions on environmental health within the One Health framework.