〔Abstract〕 Objective To investigate the predictive value of serum homocysteine(HCY) level on the risk of miscarriage in polycystic ovary syndrome(PCOS) patients undergoing frozen-thawed embryo transfer(FET). Methods 536 PCOS patients and 550 non-PCOS patients with fallopian tube factors(control group) retrospectively were analyzed.The basic characteristics and pregnancy outcomes were compared between the two groups.Also, the basic characteristics between the miscarriage group and the live birth group in PCOS patients were compared.The predictive value of Hcy on the miscarriage of PCOS patients after FET treatment was analyzed. Results Compared with the control group, body mass index(BMI),testosterone(T),Hcy, fasting insulin(FINS),homeostasis model assessment of insulin resistance(HOMA-IR),total cholesterol(TC),number of retrieved oocytes and miscarriage rate increased in PCOS group, while high density lipoprotein-cholesterol(HDL-C),high-quality embryo rate and live birth rate decreased, and the differences were statistically significant(P<0.05).Among PCOS patients, Hcy, FINS and HOMA-IR increased in the miscarriage group compared with live birth group, and the differences were statistically significant(P<0.05).Hcy, FINS and HOMA-IR were independent risk factors for miscarriage in PCOS patients, and the predictive value of Hcy for miscarriage in PCOS patients was greater than FINS and HOMA-IR,and the area under ROC curve(AUC) was 0.829(95%CI=0.755-0.902,P<0.001),the cut-off value was 15.975 μmol/L with a 79.0% sensitivity and a 87.4% specificity, which indicated high predictive value for miscarriage in patients with PCOS. Conclusion Serum Hcy level significantly increased in PCOS patients, which has an important predictive value for miscarriage after FET treatment.