Abstract: Objective To investigate the effect of body mass index(BMI)on pregnancy outcomes and perinatal outcomes in patients with polycystic ovary syndrome(PCOS)undergoing in vitro fertilization-embryo transfer(IVF-ET). Methods The infertile patients(486 cycles in total)with PCOS who received IVF-ET for pregnancy and fresh embryo transfer were selected as research objects. According to their body mass index(BMI), they were divided into control group(normal weight, BMI<24 kg/m², 173 cycles)and study group(obese, BMI≥24 kg/m², 313 cycles). The laboratory key indicators of controlled ovarian hyperstimulation, pregnancy outcomes and perinatal outcomes were compared between the two groups. Results Compared with the control group, the days of exogenous gonadotropin(Gn)application was significantly longer, total dosage of Gn group was significantly more, and the number of eggs obtained as well as the number of high-quality embryos in the study group were significantly less than those in the control group(P<0.05). The clinical pregnancy rate of the study group was significantly lower, the incidence of abortion and gestational diabetes mellitus were higher, and neonatal weight was significantly larger compared with the control group(P<0.05). Conclusion High BMI will adversely affect the related indicators of IVF-ET in infertile patients with PCOS. Taking effective measures to reduce the weight of PCOS patients in advance can significantly improve the pregnancy and perinatal outcomes.