Abstract: Objective To explore whether a high serum estradiol (E2) level before progesterone administration adversely affects the pregnancy outcomes of frozen-thawed embryo transfer (FET) cycles. Methods We retrospectively analyzed 205 hormone replacement therapy (HRT)-FET cycles in our Center between February, 2017 and August, 2017. With a cutoff value of serum E2 level of 600 pg/mL before progesterone administration, the cases were divided into high E2 level group and control group with normal E2 level, and the clinical characteristics and pregnancy outcomes were compared between the two groups. Results No significant difference was found between the two groups in the patients’age during IVF/ICSI cycle, body mass index (BMI) or endometrial thickness at the time of FET (P>0.05). The patients with high E2 levels had a significantly younger age (P<0.05) and a significantly longer duration of estradiol administration than those in the control group (P<0.05). The clinical pregnancy rates, ongoing pregnancy rates, early miscarriage rates, late abortion rates and live birth rates were all comparable between the two groups (P>0.05). After controlling for the compounding factors including the age at FET cycle and the duration of estradiol administration, all these pregnancy outcomes were still comparable between the two groups. Conclusion A high serum E2 level before progesterone administration does not adversely affect the pregnancy outcomes of HRT-FET cycles.