Objective To evaluate the clinical outcomes and report the second-look arthroscopic findings of reconstructed anterior cruciate ligament (ACL) using deep-frozen allograft.Methods Sixty-six patients undergoing ACL reconstruction using deep-frozen allograft in our institute with at least twelve months follow-up from January 2012 to March 2016 were included and received second-look arthroscopy.The patients consisted of 51 males and 15 females with an average age of 30.6 years (range,18 to 55 years) at the time of ACL reconstruction.Knee functions were evaluated by Lysholm score and International Knee Documentation Committee (IKDC) score.Knee stability was evaluated by drawer test,Lachman test and KT-1000 arthrometer.Second-look arthroscopic evaluation was performed in all patients,focused on continuity of the reconstructed ACL,the synovial coverage and subjective tension of the graft,and the prevalence of cyclops-like lesion and other changes after reconstruction procedures.Resuits All patients were followed up for average 18.3 months (range,12 to 36 months).Thirty-one patients underwent second-look arthroscopy from 12 to 18 months,and the other 35 patients underwent second-look arthroscopy from 18 to 36 months after ACL reconstruction.No infection,rejection reaction and other serious complication were reported after operation.The knee range of motion was normal in all cases,except that 10° extension limitation in one case.The Lysholm score significantly improved from preoperative 54.95±9.01 to 12 months postoperatively 86.14±5.86,and the IKDC improved from 54.79±9.12 to 85.11±5.77.Lachman test was positive in 8 cases,but negative in 58 cases postoperatively.KT-1000 arthrometer measurement showed that the side-toside difference significantly improved from preoperative 6.70± 1.24 mm to postoperative 1.52± 1.02 mm.Complete discontinuity occurred in 2 cases of the reconstructed grafts,graft tear in 4 cases.Cyclops-like mass was identified in 2 cases.The overall synovial coverage was slightly better in the patients who were followed up more than 18 months than those less than 18 months.However,there was no significant difference among the groups in the field of graft tension.The patients with taut grafts showed statistically better KT-1000 values (1.14±0.35 mm) than those with lax grafts (2.95±1.38 mm).Conclusion Frozen allograft could be a reasonable choice for ACL reconstruction.However,the graft integration and remodeling could tend to be slow.