Background: Dienogest is a progestin with demonstrated efficacy in the treatment of endometriosis in European women. The objective of this study was to evaluate the efficacy and safety of dienogest in Chinese women. Patients and Methods: This 24-week, randomized, double-blind, placebo-controlled multicenter (n=23) study evaluated the efficacy and safety of 2mg dienogest once daily in 255 Chinese women aged 18-45 years with laparoscopically diagnosed endometriosis and an endometriosis-associated pelvic pain (EAPP) score 30mm on a 0-100mm visual analog scale. The primary efficacy variable was absolute change in EAPP from baseline to week 24. Secondary efficacy variables included proportions of responders and intake of supportive analgesic medication. Safety variables included adverse events (AEs), laboratory parameters, and bleeding patterns. Bone mineral density (BMD) was evaluated in a subset of 140 women. Results: After 24 weeks of treatment, the difference between treatment arms for mean reduction in EAPP was statistically significant in favor of dienogest (-24.54mm; 95% CI -29.93 to -19.15; p<0.0001). Secondary efficacy analyses supported the significant superiority of dienogest over placebo. Dienogest was well tolerated, with few AEs associated with therapy. Dienogest had no effect on BMD levels after 24 weeks of treatment. Conclusions: Dienogest 2mg once daily for 24 weeks was superior to placebo in reducing EAPP and was safe and well tolerated in Chinese women with endometriosis. The results are consistent with studies previously conducted in European women.