Objective: Levonorgestrel releasing intrauterine system (LNG-IUS) has been shown to treat patients with non-atypical & atypical endometrial hyperplasia (EH) successfully in many western studies. Our purpose was to examine the effectiveness of LNG-IUS in the treatment of Korean women with EH. Methods: We conducted a prospective observational study of 12 women diagnosed with EH and treated with LNG-IUS insertion between February 2007 and August 2009 at the Department of Gynecology of Gangnam CHA Hospital, CHA University School of Medicine. Baseline endometrial biopsies were done before insertion of LNG-IUS, and outpatient follow-up endometrial biopsies were undertaken at 3-month intervals after insertion of LNG-IUS. We investigated the regression rate and the time to regression. Results: Four patients had simple hyperplasia without atypia, 7 patients complex hyperplasia without atypia, and just 1 patient complex atypical hyperplasia. Complete regression of EH was achieved in all cases (100%, 12/12), with the significant proportion (66%, 8/12) achieving it within 3 months. The mean duration to regression was 4.5 months. All cases had regression within 9 months. In the case of complex atypical hyperplasia, the regression was attained at the 9th month after insertion of LNG-IUS. The mean follow-up duration was 12 months (range, 3 to 27 months). As long as LNG-IUS was maintained, the EH did not recur. Conclusion: LNG-IUS appears to be as highly effective in treating Korean women with EH.