Objective To establish an effective method for superovulatory treatment of rats with pregnant mare serum gonadotrophin(PMSG) and human chorionic gonadotropin(hCG). Methods Sprague-Dawley rats at different age(4-5 weeks,67 weeks and 8-9 weeks) were superovulated with PMSG and hCG at a dosage of 10 IU, 20 IU,30 IU,40 IU or 50 IU,respectively.The results of superovulation of those rats were analyzed.Finally,the 2-cell embryos fertilized in vivo were transferred to recipients to observe the rate of pregnancy.Results Rats aged 4-5 weeks showed the best effect of PMSG/hCG at a dosage of 20 IU on superovulation,with an average number of 54.6 per rat,while rats aged 6-7 weeks and 8-9 weeks were 32.7 and 21.5 per rat,respectively.After embryo transfer,the rate of pregnancy was 63.3%,showing no significant difference with that of control rats(60%).Conclusion Rats at 4-5 weeks of age are more sensitive to superovulation,giving a highest number of oocytes with 20 IU PMSG and hCG.Such oocytes obtained by superovulation are good in quality and can complete the whole term development after fertilized in vivo and embryo transfer.