Objective: To evaluate the effect of combined therapy of Chinese herbal medicine and compound cyproterone acetate (CPA) in treating non-obesity polycystic ovarian syndrome (PCOS) and to explore its mechanism in improving withdrawal ovulation. Methods:Eighty-six patients of non-obesity PCOS, typed as Shen-deficiency with blood stasis Syndrome or Shen-deficiency with Phlegm-Dampness Syndrome by Syndrome Differentiation in traditional Chines medicine, were randomly divided into three groups: (1) The TCM group (n=26) was treated with Chinese drugs for 6 menstrual cycles; (2) The western medicine (WM) group (n=30) was treated with 1 tablet of CPA for 21 days, with the treatment beginning from the 5th day of menstruation. The treatment was given for 3 menstrual cycles by repetitious medication, which stopped and restarted on the 5th day of withdrawal bleeding. Then the ovulation promoting therapy was applied by using clomifene citrate and human chorionic gonadotropin (CC/Hcg) for 3 menstrual cycles; (3) The TCM-WM group (n=30) was treated with the medications used for the above two groups. The menstrual cycle, the volume and duration of the menstruation, as well as the improvement of acne and pilosis [Ferriman-Gallway (F-G) scoring]were observed after 3 cycles ended. Moreover, condition of ovulation was monitored by B-ultrasonography at the 4th-6th cycle and status of pregnancy was observed. Results: Compared with before treatment, the blood level of luteinizing hormone (LH) and testosterone (T) in all 3 groups after treatment significantly decreased (P<0.05), with its ratio to follicle-stimulating hormone (LH/FSH) recovered to normal, but without markedly change in levels of FSH, estradiol (E2) and prolactin (PRL). The menstrual cycle in most patients got regular and acne significantly alleviated (P<0.05), and the improvement of infrequent menstruation and acne was better in the WM group and the TCM-WM group than that in the TCM group, but pilosis showed no significant improvement in all three groups. The periodical ovulation rate in the TCM-WM group (73.1%) and the WM group (68.3%) was significantly higher than that in the TCM group (40%). The pregnancy rate in the TCM-WM group (53.8%) was significantly higher than that in the other two groups (26.1% and 25% respectively, all P<0.05). Conclusion: Using combined therapy of TCM and composite CPA followed by ovulation promoting agents of TCM and WM to treat patients of non-obesity PCOS could relieve the clinical symptoms, improve the abnormal blood level of sex hormones and significantly elevate the pregnancy rate.