Abstract: chlorpyrifos (CPF) is an organophosphate pesticide that exhibits adverse effects on male reproductive performance. In this study, its influence on reproductive function in male offspring was investigated by gestational exposure of mother mice to CPF. 10 mg/kg body weight (b.w.) of CPF or vehicle was gavaged to mother mice from the 7^th day of pregnancy to the day before delivery, and blood and testes samples from male offspring at 42 days old were collected for analysis. The content of testosterone (T) and luteinizing hormone (LH) in serum were determined by ELISA. And mRNA expression of five genes related to testosterone synthesis in testes were analyzed by RT-qPCR. Compared with the control group, prenatal exposure of CPF resulted in a 16.5% increase in the weight of testis in the offspring (P<0.01). The levels of testosterone and luteinizing hormone in serum were increased by 9.9% and 6.2%, respectively, but the difference was not significant (P>0.05). The mRNA expression level of genes related to testosterone synthesis in testes was increased significantly (P<0.01). Specifically, the expression level of HMG-CoA synthase was increased by 72.9%, and that of StAR was increased by 45.3%. In addition, the expression levels of P450scc, P450-17α, and 3β-HSD were increased by 95.5%, 68.9%, and 112.0%, respectively. These results showed that prenatal exposure to CPF could exert its toxicity to male offspring by affecting mRNA expression of genes related to testosterone synthesis.