Cnidium monnieri has been documented in traditional medicine to be effective in the treatment of male reproductive disorders. Objective of the study was to evaluate the effects of OS35 (the alcohol extract of Cnidium monnieri in which osthole is about 35 percent) on the weight of reproductive organs, amount and activity of sperms and the fertility of female rats mated with valproat exposed male rats. The result showed that OS35 at the dose of 150 mg/kg/day increased the amount and activity of sperms in male rats, increased the rate of pregnancy, fetus implantation and decreased the number of early/late dead fetuses in female rats. In conclusion, OS35 at the dose of 150 mg/kg/day reduced the reproductive toxicity induced by natri valproat in male rats.