Abstract Background: The absence of each parent impairs the psychological and social adjustment of single-parent adolescents. The objective of this study was to investigate the effectiveness of group-based dialectical behavior therapy in reducing aggression and increasing social adjustment of single-parent adolescents. Methods: The research method was quasi-experimental using a pre test and post-test design with a control group. The statistical population included single-parent adolescent boys in the junior high schools of Baghmalek city. The sample consisted of 24 students who were randomly assigned to the experimental and the control groups. The experimental group received dialectical behavioral therapy during eight sessions. The research instruments included Ahwaz aggression questionnaire (AAI) and Bell’s adjustment inventory (BAI). Data were analyzed using descriptive statistics (mean and standard deviation) and inferential statistics (multivariate analysis of covariance). The significant level was set at 0.05. Results: Findings showed that group-based dialectical behavior therapy reduced aggression and increased social adjustment of the experimental group compared to the control group (Pvalue
