Objective: This article depicts a multi-family group therapy model based on purposeful parenting concept. The aim of this study was to investigate the effectiveness of purposeful based multi-family group therapy on self-concept and problematic behaviors of adolescents. Methods: Participants included 24 junior girl students and their parents that were randomly assigned to experimental and sham-control groups, and 10 girls that waiting for the treatment in control group. 13 weekly intervention of multi-family group therapy were conducted. Self-concept and problematic behavior of adolescents was assessed before, after and 60 day later than the intervention Results: Results showed that self-concept of adolescents increased after purposeful based multi-family group therapy in experimental group and moderation of intra-family relationships that was result of the intervention, effects problematic behaviors in girls. Conclusion: Multi-family group therapy is the applied method for clinicians in adolescent‟s therapy especially in the field that problematic relationships among family and inefficient parenting cause to problematic behaviors in adolescents. The study can be the guideline for clinician that work with families and adolescents to reconstruct the family relationships with the aim of family and adolescent‟s success and satisfaction. Keywords

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