Abstract： Objective： To observe the clinical effect of modified Longdan Xiegan tang for polycystic ovary syndrome(PCOS) and its effect on sex hormone levels. Methods： A total of 210 cases of PCOS patients were selected for retrospective study，and divided into the observation group and the control group according to different treatment measures，with 105 cases in each group. The control group was treated with ethinyl estradiol cyproterone tablets，and the observation group was additionally treated with modified Longdan Xiegan tang. Both groups were treated for three menstrual cycles. Results： The total clinical effective rate was 96.2% in the observation group and 87.6% in the control group， the difference being significant(P＜0.05). Before treatment，there were no significant difference being found in the comparison of the levels of follicle stimulating hormone(FSH)，luteinizing hormone(LH)，LH/FSH，prolactin(PRL)，free testosterone(FT) and androstenadione(A) in serum between the two groups(P＞0.05). After treatment，the levels of FSH，LH，LH/FSH，PRL，FT and A in the observation group were significantly decreased when compared with those before treatment(P＜0.05)；the levels of LH，LH/FSH，FT and A in the control group were significantly decreased when compared with those before treatment(P＜0.05)； PRL level in the observation group was significantly lower than that in the control group(P＜0.05). There was no difficant in the levels of FSH、LH、LH/FSH、FT and A between two groups(P＜0.05). The incidence of adverse reactions was 23.8% in the control group， and no obvious adverse reaction was observed in the observation group， the difference being significant(P＜0.05). Conclusion： Modified Longdan Xiegan tang for PCOS has a satisfactory curative effect， which can effectively improve the levels of sex hormones in patients without obvious adverse reaction.