Abstract： Objective To evaluate the efficacy and safety of focused ultrasound ablation in the treatment of submucosal fibroids which broke into uterine cavity less than 50%. Methods From Oct. 2006 to Sept. 2009, 66 patients with 69 submucosal fibroids broke into uterine cavity less than 50% diagnosed by MRI in Chinese People's Liberation Army General Hospital were enrolled in this study. They were treated by ultrasound-guided focused ultrasound ablation in the outpatient department, which using the contrast enhanced ultrasonography to assess the efficacy after ablation immediately, to measure reduction of fibroids volume and record adverse effect before and after ultrasound ablation. At 3, 6, 12 and 24 months after treatment, ablation outcome and fibroids volumes were evaluated by contrast ultrasound. The changes of clinical symptom were evaluated by the symptom severity score ( SSS) of the uterine fibroid quality-of-life instrument( UFS-QOL). Results The average volume of fibroids in 66 patients with 68 submucosal fibroids were (151 ±134) cm3 before treatment and (114 ± 104) cm3 no enhanced regional after treatment. The ablation rate of target fibroids was (77 ±16)%. All patients completed this treatment successfully, they were followed up for 6 - 44 months, the median follow-up time was 24 months. No serious complication was observed. However, there were 52% (34/66) patients presented vaginal discharge after ablation, it disappeared gradually after 3 to 4 menstrual cycles. The SSS and the menstrual period symptom scores were significantly lower than that before ablation at the follow-up of 3,6, 12 and 24 months, the rates were 20. 9% , 38. 0% , 45. 1% , 47. 1% and 42. 0% , 63. 8% , 64. 2% , 68. 8% , which all reached statistical difference (P ＜ 0. 05 ). The necrotic fibroids were absorbed gradually, the reduction rates of fibroid volume were 44. 7% ,66. 0% ,77. 7% and 89. 8% . Conclusion It was safe and efficacy that focused ultrasound ablation was used in treatment of submucosal fibroids which broke into the uterine less than 50%.