Microplastics are being widely discussed as an emerging global environmental contaminant. Microplastic pollution usually originates from land-based sources, which are then mainly transported through hydrological and atmospheric pathways and accumulated in terrestrial, freshwater and marine ecosystems. Urban environments represent a condensed area of human activities (including the production and use of plastic materials), and urban rivers may therefore be a key transporter of microplastic pollution. Understanding microplastic abundances in urban rivers is potentially important in finding effective means of reducing fluvial microplastic discharge. This study quantified microplastic abundances in surface waters along the Fenghua River, Ningbo, a coastal megacity in East China. Microplastic pollution was distributed unevenly along the river, with concentrations ranging from 300 n/m³ to 4000 n/m³ (0.3 – 4.0 n/L). Average concenterations were 1620.16 ± 878.22 n/m³ (1.62 ± 0.88 n/L) in summer (43 sampling points) and 1696.08 ± 983.52 n/m³ (1.70 ± 0.98 n/L) in winter (17 sampling points). The most common microplastic shapes, sizes, colors and types of polymers were fiber, <0.5mm, transparent and polypropylene, respectively. Using multidimensional scaling analysis, microplastic distribution patterns were related to seasonal factors and levels of urbanization. No clear relationships were found, with implications for site selection when studying microplastics and the challenges of attributing sources to microplastic pollution in urban rivers.