Abstract: In this paper, the effect of single and combined exposure of polystyrene microplastics (PS-MPs) and clothianidin on the germination characteristics of maize seeds was investigated. The results showed that the germination of maize seeds (germination rate, germination energy, germination index, vigor index, root length, and shoot length) was significantly inhibited by 10 mg/L and 100 mg/L PS-MPs with three particle sizes of 0.5, 5, and 50 μm in the single treatment, and the variation in particle size and concentration of PS-MPs had less effect on the germination status of maize seeds. In the single clothianidin treatment, the low concentration (10 mg/L) of clothianidin had no significant effect on the germination of maize seeds, while the high concentration (100 mg/L and 200 mg/L) of clothianidin had a significant inhibitory effect on the germination of maize seeds. Compared with single clothianidin treatment, the combined exposure group with the 100 mg/L PS-MPs with a particle size of 50 μm and 200 mg/L clothianidin decreased the content of clothianidin in maize seeds, alleviating the inhibitory effect of high concentrations of clothianidin on the germination of maize seeds. High concentrations of clothianidin and single PS-MPs exposure inhibited maize seed germination, whereas PS-MPs alleviated the inhibitory effects of high concentrations of clothianidin on seed germination in the combined exposure.