〔Abstract〕 Objective To investigate the relationship between insulin resistance and the serum level of mesencephalic astrocyte-derived neurotrophic factor(MANF) in patients with polycystic ovary syndrome(PCOS). Methods There were 120 patients with PCOS and 40 healthy women recruited as the experimental group and the control group respectively.The serum levels of sex hormones, fasting blood glucose(FBG),fasting insulin(FINS),and MANF in the experimental group and the control group were compared.The serum MANF level of patients with or without insulin resistance in the experimental group was also compared and the relationship between homeostasis model assessment for insulin resistance(HOMA-IR) and the serum MANF level was analyzed. Results Compared to the control group, the serum levels of luteinizing hormone, testosterone, androstenedione, dehydroepiandrosterone sulfate, FBG,FINS,and HOMA-IR in the experimental group were significantly higher(P<0.05),whereas the serum levels of follicle stimulating hormone, sex hormone binding globulin, and MANF were significantly lower(P<0.05).Compared to patients without insulin resistance(59 cases),the serum MANF level of patients with insulin resistance in the experimental group(61 cases) was significantly lower(P<0.05),and there was a negative correlation between the serum MANF level and HOMA-IR of PCOS patients in the experimental group(P<0.05). Conclusion MANF possibly plays an important role in the occurrence and progression of insulin resistance in PCOS patients, which will be able to provide new approaches to the diagnosis and treatment of PCOS.