Abstract: Objective：To study the efficancy and long possible mechanism of Mirena（levonorgestrel intrauterine system）in the treatment of simple endometrial hyperplasia. Methods：Select sixty cases of simple endometrial hyperplasia in outpatient between 2011.11 and 2012.2，we observed the menstrual patterns，the endometrial thickness and uterine arterial blood flow [resistance index（RI），pulsatility index（PI）] by transvaginal ultrasound，pathologic changes of endometrial by endometrial biopsy in 6 months after insertion of mirena. Results：2 patients were removed Mirena due to colporrhagia. Pathological examinations of 58 patients performed 6 months after the insertion showed that endometrial hyperplasia had reversed. The endometrial thickness，RI of uterine artery in 6 months after the insertion were statistically significant，respectively（1.52±0.33） cm，（0.62±0.14） cm（P＜0.05） and 0.64±0.07，0.79±0.08（P＜0.01）；PI was 1.98±0.51，1.96±0.04，the difference was not statistically significant（P＞0.05）. After placing Mirena significantly reduced by the amount，24 cases showed oligomenorrhea，32 cases showed amenorrhea. Conclusions：Mirena is an efficient and simple treatment of simple endometrial hyperplasia. The influence of uterine arterie blood flow is its possible mechanism.

Key words: Endometrial hyperplasia, Levonorgestrel, Intrauterine devices, Delayed-action preparations, Hemodynamics