Although more attention has been paid to plastic pollution in marine ecosystems, research on the influence of plastic in freshwater ecosystems remains limited. To help fill this information gap, this article represents an investigation of the effects of virgin polyvinyl chloride (v-PVC) microparticles (MPs) and UV-aged polyvinyl chloride (a-PVC) MPs on the growth and chlorophyll content of the freshwater algae, Chlamydomonas reinhardtii (C. reinhardtii) at different periods (0, 24, 48, 72 and 96 h). The results suggest that both virgin and aged PVC MPs have negative effects on the growth of C. reinhardtii in the range 01 10 mg/L to 200 mg/L, which leads to the reduction of chlorophyll-a level in the cells. Furthermore, a-PVC MPs were more toxic than v-PVC MPs, as shown by the a-PVC MPs lower EC50 values after 96 h (63.66 mg/L for a-PVC MPs and 104.93 mg/L. for v-PVC MPs). The inhibition effect of both kinds of PVC was also testified by the enhancement of enzymatic activity of superoxide dismutase (SOD) and malondialdehyde (MDA) in algae. Meanwhile, a-PVC MPs obviously had a higher toxicity than v-PVC MPs. The aging process that affected the surface characteristics of a-PVC was identified using Fourier transform infrared (FUR) and Zetasizer. The carbonyl groups formed on the surface and the increased zeta potential of the a-PVC MPs affected the interaction between the microplastics and the algae, which increased the toxicity of aged microplastics. The research results presented here provide more evidence of the risks microplastics bring into the freshwater ecosystem.