This study aimed to evaluate the respective effects of mifepristone or quinestrol on the reproductive organs and sex hormones of female Mongolian gerbils.Mifepristone (4 mg/kg) or quinestrol (4 mg/kg) was administered by gastric gavage (0.8ml) for 3 consecutive days to 6 groups (n=8 per group) plus a control group,which was administered with an equal volume of oil only.Females were killed at 5,10,and 15 days after mifepristone or quinestrol treatment.Mifepristone did not affect the body mass,uterine and ovarian weights,or progesterone concentration.However,their serum estradiol concentration at 10 and 15 days was significantly higher compared to at 5 days.Conversely,quinestrol significantly increased uterine weight and increased the serum estradiol concentration at 5 and 10 days,and progesterone concentration at 5 days.However,body and ovarian weight did not change.The uterine and ovarian weights and serum progesterone in the mifepristone-treated groups were significantly lower than that in the quinestrol-treated groups at the same time after treatment.However,estradiol concentration exhibited a different phenomenon: after quinestrol treatment,estradiol was higher than in the mifepristone-treated group at day 5,was similar in both groups at day 10,and was lower in the quinestrol-treated group at day 15.Therefore,while mifepristone influenced the normal reproductive indices in Mongolian gerbils,quinestrol exhibited a better contraceptive effect than mifepristone.