OBJECTIVE To evaluate the efficacy and safety of dydrogesterone in the treatment of dysmenorrhea. METHODS The prospective ，random-controlled，open-labeland multicenter clinical study was adopted. A total of 108 women with dysmenorrhea were randomly assigned into dydrogesterone group and control group according to the ratio of 1∶1，with 54 patients in each group. Dydrogesterone group was treated with dydrogesterone 10 mg orally ，twice a day ，on the 5th-25th day of menstrual cycle ，for 3 menstrual cycles. Control group received Guizhi fuling capsule 0.93 g orally ，three times a day，since the end of menstrual bleeding to the third day of the next menstruation ，for 3 menstrual cycles. Main results were the changes of visual analogue scale （VAS）scores in 2 groups after 3 menstrual cycles ；secondary results were the changes of COX menstrual symptom scale （CMSS），quality life of 36-item short form （SF-36），levels of carbohydrate antigen 125（CA125）and interleukin 6（IL-6）after 3 menstrual cycles ；other findings included additional benefits and drug safety. RESULTS The results of intention to analysis data set and the follow-up study protocol analysis data set showed that VAS scores of 2 groups after treatment of dysmenorrhea for 1，2 and 3 menstrual cycles were lower than those before treatment ，the longer the treatment time ，the more obvious the decrease of VAS score （P＜0.05），and VAS score decline of dydrogesterone group was better than that of control group（P＜0.05）. After 3 menstrual cycles ，both the two group showed significant reduction in the severity and duration scores of CMSS（P＜0.05）；and the decrease of the above scores in the dydrogesterone group was superior than in the control group （P＜ 0.05）. After 3 menstrual cycles ，among 8 dimensions of SF- 36 scale，the scores of 7 dimensions in dydrogesterone group were significantly higher than those before treatment ，such as the scores of physiological function ，physical role ，physical pain ， emotional function ，social function ，general health status and energy （P＜0.05）；the increase of the scores of four dimensions were higher than those in the control group ，such as physical pain ，social function ，general health status ，energy（P＜0.05）. There was no significant difference in the levels of CA 125 and IL- 6 between 2 groups before and after treatment （P＞0.05）. After 3 menstrual cycles，the menstrual cycle and menstrual period in the dydrogesterone group were shorter than those before treatment ，and the menstrual volume decreased （P＜0.05）；but there was no significant change in the above indexes of control group （P＞0.05）. After 3 menstrual cycles ，the incidence of adverse drug events and adverse reactions in dydrogesterone group was 32.69％（17/52）and 28.85％（15/52）；no serious adverse drug events or adverse reactions such as thrombosis occurred in both groups. CONCLUSIONS Dydrogesterone can effectively reduce the VAS score ，also relieve dysmenorrhea-related symptoms ，and improve the quality of life. The efficacy of dydrogesterone is superior than that of Guizhi fuling capsule in treatment for dysmenorrheal ，without serious adverse reactions. It is well tolerated.