The goal of this research was to investigate the effectiveness of Acceptance and Commitment Therapy (ACT) on treatment of adolescents with major depression disorder. The research method was quasi-experimental with
pre-test, post-test, and follow-up with a control group. According to the inclusion criteria, 16 female adolescents with major depression disorder were selected through available sampling method and randomly assigned into two 8-member experimental and control groups. Before starting intervention, Beck Depression Inventory-II was conducted in pretest of each two groups. Afterwards, eight 60-90 minutes sessions of ACT were executed to treat experimental group. Then the posttest for each group was performed and two months after posttest, the follow-up were carried out for each group. Data were analyzed using SPSS-23 software and analysis of variance with repeated measures statistical method. The findings showed that ACT has a significant effect on treatment of adolescents with major depression disorder (P< 0.05). This also persisted in the follow-up period (P>0.05). The use of Acceptance and commitment therapy for the treatment of adolescents with major depression is recommended to all psychologists, consultants, and psychiatrists.