Abstract: Objective To observe the toxic effect of ethaselen on the ability of maturity,mating,fecundity and the growth and development of fetation.Methods Sprague-Dawley rats were randomly allocated into 0,250,500 and 1000 mg/kg dose groups,and given ethaselen orally 8 weeks formale rats,2 weeks for female rats,respectively,and mated 2 oestrams The ethaselen treahnent continued until 14th day of pregnancy and the ovary,uterus and embryo of the female rats were observed When the female rats were fecundated,the male rats were executed and their testicles and epididymides were observed Results The rats in treatment groups were nounal in spirit,behavior and hair but the body weight accretion was sloe.The genitalia development,sex function,the quantity and quality of speun of the male rats were natural The num ber of live embryo (nest average most value-6.8) decreased The absorbed embryo (nest average most value +5.9) and the lost ratio of oospeun in pregnancy rats(> 54%)increased There was no significant difference in the ratio of mating and pregnancy,the number of corpusluteum,plant gland and death embryo,the fetus body weight and abnoun ality between the treatment and the control groups Conclusion Within the range of experinent doses,ethaselen obviously decreases body weight accretion of male rats,increases the fetation hypogenesis in gestation nonage and the lose ratio of zoospeun in pregnancy rats but does not affect the development of genitalia,mating behavior,speun and ovummature and live fetus.