Background & objectives: Aedes albopictus and Culex pipiens pallens are important vectors of many viruses and have had resistance to chemical pesticides. Spinosad is a selective biological insecticide to control urban mosquitoes. The aim of this study was to reveal the sublethal effects of spinosad on mosquitoes and provide reference basis for integrated mosquito management. Methods: The toxicity of spinosad against Ae. albopictus and Cx. pipiens pallens was determined under laboratory conditions by exposing early third-instar larvae to different concentrations. Results: The LC50 values of spinosad to Ae. albopictus and Cx. pipiens pallens larvaes were were 4.44×10-3 mg·L-1 and 1.93×10-3 mg·L-1 respectively after 72 h exposure. Spinosad at sublethal concentrations has many negative effects on Ae. albopictus and Cx. pipiens pallens larval, pupae, adult and offspring eggs, including significantly reduced their larvae pupation rate by 51.37% and 58.47%, significantly prolonged pupae length by 21.43% and 16.18%, reduced female wing-spans by 20.19% and 14.89%, reduced male wing-spans by 3.84% and 7.54%, reduced female weight by 29.04% and 31.52%, reduced male weight by 7.47% and 9.07%, reduced female and male ratio by 51.98% and 45.21%, reduced individual egg-laying amount by 15.73% and 35.51%. In addition, offspring egg hatchability were dramatically decreased by 25.71% and 34.04%, egg periods were significantly prolonged by 14.42% and 62.82%, respectively. No significant effect on larval period, pupae emergence rate, female bite rates was observed. Interpretation & conclusion: These results suggest that spinosad might affect pest population dynamics significantly and is fairly expected to be a candidate biological pesticide for mosquito control.