Abstract: Polycystic ovary syndrome （PCOS） affects 6.6%-6.8% of women in reproductive age. Insulin resistance and hyperinsulinemia play a critical role in the pathogenesis of PCOS, which are associated with a high risk of type 2 diabetes mellitus and cardiometabolic abnormalities. According to its mechanism, metformin can improve insulin sensitivity，reduce hyperinsulinaemia and mediate other clinical symptoms of adult PCOS patients. Metformin is mainly used for losing weight，alleviating insulin resistance，regulating the menstrual period, and treating infertility. In puberty PCOS patients, metformin is used for reducing cholesterol，triglycerides，abdominal and visceral fat. In PCOS women with pregnant, metformin can lower the risks of gestational diabetes，gestational hypertension，preeclampsia, and improve neonatal outcome without any serious side effects. Overall，many available data supported that metformin could lower the cardiometabolic risk , and improve reproductive outcome, in PCOS women.

Key words: Polycystic ovary syndrome, metformin, Insulin resistance, Menstrual disorder, Infertility, Gestational diabetes mellitus