Objective The efficacy of prophylactic aneurysmal sac embolization is still unclear.The purpose of this study is to evaluate the safety and efficacy of prophylactic aneurysmal sac embolization with N-butyl cyanoacrylate(NBCA)during endovascular aortic repair(EVAR)in patients with abdominal aortic aneurysms(AAA)so as to prevent the occurrence of type Ⅱ endoleak.Methods The clinical data of patients with AAA,who received EVAR from January 2019 to January 2022 at Gansu Provincial Hospital,were retrospectively analyzed.According to the strict inclusion and exclusion criteria,a total of 74 AAA patients were enrolled in this study.Of the 74 AAA patients,intraoperative prophylactic injection of NBCA into the aneurysmal sac to embolize the sac cavity during EVAR was performed in 36(study group),while standard EVAR treatment was carried out in 38(control group).The clinical data of the 74 patients,mainly including age,gender,underlying diseases,diameter of the aneurysm,hospitalization cost,time spent for surgery,type of stent,mode of anesthesia,etc.were collected.The primary endpoint was the incidence of endoleak during follow-up period,and the secondary endpoints included the rate of endoleak-related re-intervention,adverse events,and mortality during follow-up period.Results Before surgery,there were no statistically significant differences in gender,age,diameter of the aneurysm[55.46(15.60)mm vs 63.15(24.00)mm],and underlying diseases between the study group and the control group,and no intraoperative complications occurred.The technical success rate was 100％in both groups.Three months after EVAR treatment,the incidence of type Ⅱ endoleak in the study group was significantly lower than that in the control group(2.86％vs 21.05％,P＜0.01);six months after EVAR treatment,the incidence of type Ⅱ endoleak in the study group and the control group was 8.82％and 28.95％respectively(P＜0.01);and 12 months after EVAR treatment,the incidence of type Ⅱ endoleak in the study group and the control group was 8.82％and 31.43％respectively(P＜0.01).In the study group a total of 4 times of re-intervention were carried out,one of which was associated with type Ⅱ endoleak.In the control group a total of 8 times of re-intervention were conducted,6 of which were associated with type Ⅱ endoleak.No statistically significant difference in the overall re-intervention rate existed between the two groups(P=0.224).The type Ⅱ endoleak-related re-intervention rate in the study group was slightly lower than that in the control group,but the difference was not statistically significant(P=0.106).Conclusion Prophylactic injection of NBCA into the aneurysmal sac cavity of AAA during EV AR procedure is a simple,safe and effective method,which can significantly reduce the occurrence of type Ⅱ endoleak in the early-middle stage and prevent the enlargement of the aneurysmal sac after EVAR,besides,it has no significant effect on the re-intervention rate and mortality,does not significantly prolong the operation time,and does not increase the dosage of contrast agent.