Abstract. Microplastics (MPs) in the environment have significantly impacted ecosystems and threatened human health. This study investigated the distribution and characteristics of MPs in the Nhue- Day River basin in Vietnam, which used to be a source of critical biodiversity and support for the economic growth of about 12 million people. The effect of seasonal variation and anthropogenic activities on the MP abundance was assessed. The findings revealed that the amount of pollution produced by MP abundance was significant in this study area. The average abundance of MPs in the dry season (754 items/m3) was higher than that in the rainy season (706 items/m3) with n=9. The range in the abundance of MPs in the dry and rainy seasons was 49-2,827 and 400-1,133 items/m3, respectively. The MPs collected in this study were mainly small-sized particles, with a significant proportion distributed in the 0.5- 2.0 mm size range. However, the present study showed that the relationship between MPs a