Objective To evaluate the efficacy and safety of the levonorgestrel-releasing intrauterine system (LNG-IUS) for the prevention of endometriosis recurrence after conservative surgery.Methods We enrolled patients with medium and severe endometriosis who underwent conservative surgical treatment.All patients were divided into 3 groups:group A in which the patients were administered with 3 cycles of gonadotropin-releasing hormone agonist (GnRH-a) 5 days postoperatively,group B in which the patients were administered with the LNG-IUS 5 days postoperatively,and group C in which the patients were administered with 3 cycles of GnRH-a 5 days postoperatively and the LNG-IUS on the day of the third GnRH-a injection.All patients were followed up at 3,6,12,and 24 months postoperatively.Dysmenorrhea relief was evaluated,and pelvic ultrasound and serum CA125 detection were performed.All treatment-related adverse reactions were recorded.Results Eighty-three patients were included with 21,29,and 33 in groups A,B,and C,respectively.The VAS scores in all 3 groups after 3 months were significantly lower than those obtained preoperatively (P ＜ 0.05).No significant difference was found in the VAS scores after 6 and 12 months among the 3 groups (P ＞ 0.05).After 24 months,the VAS scores in group A were significantly higher than those in the other 2 groups (P ＜ 0.05).Endometriosis recurrence was found in 8 patients after 24 months,with 4 (19.05％),3 (10.71％),and 1 (3.13％) such patient in groups A,B,and C,respectively (P ＜ 0.05).No serious side effects were found.Conclusion Postoperative application of LNG-IUS can effectively prevent recurrence and relieve pain caused by endometriosis,and its combined application with GnRH-a can improve efficacy.