Abstract: Wastewater treatment plants in coastal cities is a main source for microplastics in the ocean.Characteristic of microplastics can improve our understandings of the impacts of human activities on the marine environment.However, there is a lack of such information in China.In this study, microplastic pollution in Xiamen Yundang Wastewater Treatment Plant was studied.We designed an improved sampling device and an experimental method to study the characteristics of microplastics in the influent, effluent and sludge.The results show that the microplastic abundance in the influent, primary and secondary treatment discharge is 1.703, 1.090 and 0.324 pieces/L, respectively.The microplastic removal rates in the primary and secondary treatment discharge are 35.99% and 80.97% respectively.The concentrations of microplastics in primary and secondary sludge are 2.14×10³ and 6.62×10³ pieces/kg, respectively.The shape of microplastics are dominated by 43.89% of fiber and 32.85% of pellet in the wastewater and 68.9% of fragment and 34.78% of pellet in the sludge.The primary colors are white (34.95%), followed by transparent (22.74%) in the wastewater.While it is dominated by yellow (39.13%), black (17.39%), and white (13.04%) in the sludge.The chemical composition is primarily composed of 21.17% of PP and 18.39% PS in the wastewater and 34.78% of PP and 26.09% of PE in the sludge.It is estimated that~9.72×10⁴ pieces of microplastics are discharged into the Xiamen West Sea each day.Our findings show that waste water treatment plants play an important role in reducing urban microplastic pollutants entering the ocean, but it requires higher microplastic removal efficiency.