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 lower 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 significant （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.