BackgroundThe major depressive disorder has high prevalence among adolescents， and non-suicidal self-injury （NSSI） behaviors frequently occur among patients， therefore， major depressive disorder in adolescents has become the researching focus. ObjectiveTo explore the effect of mentalization-based family therapy （MBFT） on depressive symptoms and NSSI behavior in adolescents with major depressive disorder， and to provide references for the rehabilitation of major depressive disorder in adolescents. MethodsA total of 90 adolescent patients with major depression disorder who met the diagnostic criteria of International Classification of Diseases， 10th edition （ICD-10） for depressive disorders and attended Wuhan Mental Health Center from January to December 2022 were selected， and were assigned into study group （n=44） and control group （n=46） using random number table method. All participants received routine intervention， based on this， study group added a 60-minute MBFT intervention once a week for 8 weeks. Before the intervention and at the end of 1^st， 2^nd，4^th and 8^th week，the two groups were assessed using Hamilton Depression Scale-24 item （HAMD-24）， General Self-Efficacy Scale （GSES）， Pittsburgh Sleep Quality Index （PSQI） and Ottawa Self-injury Inventory （OSI）. ResultsThe repeated measures analysis of variance reported a statistical main effect of time， main effect of group， and interaction effect between time and group at the baseline and the end of 1^st， 2^nd， 4^th and 8^th week of treatment in HAMD-24 score （F=69.621， 15.428， 29.623， P˂0.05）， OSI score （F=176.642， 37.682， 21.873， P˂0.05）， GSES score （F=215.236， 57.421， 27.857， P˂0.05） and PSQI score （F=268.541， 61.863， 33.867， P˂0.05）. Individual effect analysis discovered a statistical difference between study group and control group at the end of 2^nd， 4^th and 8^th week of treatment in HAMD-24 score （t=5.567， 8.645， 6.233， P˂0.01）， OSI score （t=3.675， 11.817， 9.632， P˂0.01）， GSES score （t=23.462， 31.709， 12.750， P˂0.01） and PSQI score （t=9.664， 22.457， 9.333， P˂0.01）. ConclusionMBFT may improve depressive symptoms， NSSI behavior， sleep quality and self-efficacy in adolescents with major depressive disorder. ［Funded by 2022 Natural Science Foundation Project of Hubei Province （number， 2022CFB483）］