Abstract: In order to explore the toxicities of polystyrene microplastics and nanoplastic with different sizes to reproduction of rotifers, the effects of polystyrene plastics with three particle sizes (100 nm, 0.5 µm, 1 µm) on the sexual reproduction of rotifer Brachionus calyciflorus were investigated in this study. The results showed that: (1) Polystyrene nanoplastics showed more acutely toxic to rotifers than microplastics. (2) Compared to the control, 20 mg/L 100 nm polystyrene nanoplastics and 0.01, 0.1, 1, 10, 20 mg/L 1 µm microplastics significantly reduced the population growth rate of rotifers (P<0.05). (3) Polystyrene microplastics and nanoplastics significantly affected the mictic rate and fertilization rate of rotifers. (4) 10 and 20 mg/L 100 nm polystyrene nanoplastics significantly inhibited the 7 d resting eggs production of rotifers, but the reverses were true for 0.1 mg/L 1 µm and 0.01, 0.1, 1, 10, 20 mg/L 0.5 µm microplastics (P<0.05). This study showed that both mictic rate and resting eggs production were suitable endpoints for evaluating the effects of polystyrene microplastics and nanoplastics on sexual reproduction of rotifers.