Objective:To compare the effect of different endometrial preparation methods on the clinical outcome of frozen-thawed embryo transfer (FET). Methods:Total 1 372 FET cycles from January 2007 to July 2009 were retrospectively analyzed and divided into two groups:natural cycle group(n=1 014)and ovulation induction cycle group(n=358). The latter was further divided into three Sub groups:HMG cycle group(n=127),clomiphene citrate + HMG cycle group(n=77) and letrozole+HMG cycle group(n=154). The patient age,duration of infertility,basal FSH,LH and E2 levels,number of embryo transferred,embryo quality and endometrial thickness,the rates of embryo implantation,biochemical pregnancy,clinical pregnancy,early abortion,late abortion and live births were compared between these different groups. Results:FET cycle outcomes were similar between the nature cycle group and the ovulation induction cycle group on early abortion rates(9.3% vs 9.8%,P > 0.05),late abortion rates (1.8% vs 1.6%,P > 0.05) and ectopic pregnancy rates(1.6% vs 0.5%,P > 0.05). There were significant differences of the rates of embryo implantation (26.7% vs 31.5%,P < 0.05),biochemical pregnancy (50.2% vs 57.5%,P < 0.05),clinical pregnancy (43.5% vs 51.1%,P < 0.05) and live births (38.0% vs 44.9%, P < 0.05) between the two groups. The clinical pregnancy rates of three ovulation induction cycle groups were 54.5%,51.9%,42.8%,respectively in letrozole+HMG cycle group,the HMG group and the clomiphene citrate+HMG group. There were no significant differences among them. Conclusion:Endometrial preparation of natural cycle or proper ovulation induction cycle are very suitable for FET.