Objective: To evaluate the effectiveness of GnRH agonist in comparison with hCG for triggering final oocyte maturation in endometrial preparation of letrozole stimulation protocols for frozen-thawed embryo transfer.Methods Retrospective cohort study,the frozen-thawed embryo transfer cycles(FET) that use the letrozole stimulation protocols for endometrial preparation were divided into two groups according the different method of triggering final oocyte maturation.Group A(n=96) that used GnRH agonist trigger;Group B(n=689)hat used hCG trigger.luteal phase support was achieved by injection of progesterone 40mg/daily.These study had no tubal fluid,endometrial polyps and no anatomical abnormalities of the uterus,between april 2008-december 2012.To comparing the patients age,and the endometrial thickness on the day of triggering ,the clinical pregnancy rates ,the miscarriage rates and live birt rates and so on.Results There were no significant differences in the age,the endometrial thickness,the number of embryos transferred between the two groups.The clinical pregnancy rate,abortion rate and live birth rates of the group A were similar compared with the group B,P <0.05.Conclusion Using GnRH agonist for oocyte triggering in endometrial preparation of letrozole stimulation protocols for frozen-thawed embryo transfer does not affect the clinical outcome compared with hCG under the same luteal phase support.