Abstract: Microplastics (MPs) are a type of emerging contaminants that pose potential threats to the stability of global aquatic ecosystem. This study aimed to analyze the distribution characteristics and composition differences of microplastics in the Wanquan river basin of Hainan Island, using 10 water samples and 9 sediment samples. The results revealed that the abundance of microplastics in the surface water of the Wanquan river was 0～1.7 items/L, while that in the sediments was 0～14.8 items/kg. The distribution of microplastics abundance in the Wanquan river showed a gradual increase from upstream to downstream and the estuary, with a sudden rise at the convergence of tributaries. Additionally, smaller microplastics (0.005～0.5 mm) were found to constitute a larger proportion in the surface water compared to the sediments. The predominant color of microplastics in the water was green, whereas in the sediments, it was mainly blue. Cellophane is the most predominant type of plastic polymer identified in microplastic samples from water bodies and sediments. In addition, small amounts of polyacrylonitrile (PAN) and polyethylene terephthalate (PET) were detected in water bodies, while polypropylene (PP), polyethylene (PE), polystyrene (PS), and polyamide (PA) were detected in sediments. In conclusion, the sources of microplastics in Wanquan river are mainly domestic sewage discharge, household and fishing waste. The abundance of microplastics in Wanquan river is generally lower than that in other major exorheric rivers, but it is still affected by human activities. This study can provide scientific basis for monitoring and risk assessment of emerging contaminants such as microplastics in exorheric river environment in tropical areas.