OBJECTIVE:To investigate the effect of metformin on sex hormone level,insulin resistance and related indexes in women with polycystic ovarian syndrome(PCOS). METHODS:79 PCOS women were collected as PCOS group,other 86 healthy women as control group. All patients received 0.85 g Metformin tablet,twice a day,for totally 6 months. Boby mass,BMI,waist circumference,hip circumference,ratio of waist to hip,glycated hemoglobin,T,DHEA-S,E2,LH,FSH,PRL,PROG,SHBG, FPG,FINS,LH/FSH,HOMA-IR and FAI before and after treatment in PCOS group were observed and compared with control group. RESULTS:During treatment,2 patients made withdrawal because of pregnancy,3 made withdrawal because of showing gastrointestinal side effects,2 were lost to follow,totally 72 completed it. After treatment,body mass,BMI,waist circumference, hip circumference,glycated hemoglobin,FINS,HOMA-IR,T,LH,LH/FSH,PROG,FAI in PCOS group were significantly low-er than before,SHBG was significantly higher than before,glycated hemoglobin and PROG were lower than control group,while waist circumference,FINS,HOMA-IR,LH/FSH and FAI were higher than control group,the differences were statistically signifi-cant (P<0.05). There was no significant difference in ratio of waist to hip,FPG,DHEA-S,E2,FSH and PRL before and after treatment(P>0.05). CONCLUSIONS:Metformin can effectively improve the sex hormone levels and insulin resistance of patients with PCOS.