Objective To compare the clinical outcomes of all-inside arthroscopic and open recon-struction of the anterior talofibular ligament(ATFL)and calcaneofibular ligament(CFL).Methods The clinical data of 51 patients with chronic lateral ankle instability(CLAI)and treated in our department between January 2017 and July 2021 were analyzed retrospectively.Among them,24 received ar-throscopic ATFL and CFL reconstruction(arthroscopy group),while 27 underwent conventional surgery(open group).The perioperative data including surgical time,intraoperative complications,hospitaliza-tion duration and time to resume normal walking were compared between the two groups.Moreover,postoperative CT examination was performed to evaluate the position of the bone tunnel.Before as well as 3 months,6 months,1 year,and 2 years after the operation,both groups were evaluated using the American Orthopedic Foot and Ankle Society Score(AOFAS),Karlsson score,visual analogue scale(VAS),drawer test,and inversion test.Meanwhile,the occurrence of complications was also recorded and compared.Results Both groups underwent the surgery successfully.The total length of incision and time to resume normal walking in the arthroscopy group were significantly shorter than the open group(P<0.05),while there was no significant difference between them in surgical time and hospital stay(P>0.05).Postoperative CT showed that in the arthroscopy group,1 case had suboptimal talus bone tun-nel position,while in the open group,1 had suboptimal calcaneus bone tunnel position and another suffered from suboptimal talus bone tunnel position,with the remaining bone tunnels located within the corresponding footprint area.All patients were followed up for 24 to 33 months.Significant improve-ment was observed in the average AOFAS score,Karlsson score,and VAS score in both groups after the operation(P<0.05),and both the drawer and inversion tests were of negative results.Three months postoperatively,the arthroscopic group had significantly better AOFAS,Karlsson and VAS score than the open group(P<0.05).Moreover,at 6 months postoperatively,the average AOFAS and Karlsson scores of the arthroscopy group were significantly superior to the open group(P<0.05).However,1 year and 2 years postoperatively,no significant differences were found between the two group in the AOFAS,Karlsson and VAS score(P>0.05).Moreover,no serious complications occurred during surgery and follow-up in both groups.Conclusion The efficacy of arthroscopic reconstruction of ATFL and CFL is comparable to open reconstruction in treating CLAI,with the former therapy resulting in faster recov-ery.