Conducted in Iran, participants included 69 adolescents with obsessive-compulsive disorder (OCD) who were on a stable selective serotonin reuptake inhibitor (SSRI) dose and were randomly assigned to one of three conditions: group acceptance and commitment therapy (ACT)+SSRI, group cognitive behavioral therapy (CBT)+SSRI, or continued SSRI treatment. Assessment occurred at pre-, post-treatment, and three-month follow-up and included the Children’s Yale-Brown Obsessive Compulsive Scale (CY-BOCS), Children’s Depression Inventory (CDI), Avoidance and Fusion Questionnaire for Youth (AFQ-8), Valued Living Questionnaire (VLQ), and Child and Adolescent Mindfulness Measure (CAMM). ACT+SSRI and CBT+SSRI conditions demonstrated significant reductions in OCD severity that were maintained at follow-up compared to the continued SSRI condition. All conditions demonstrated significant reductions in depression that were maintained at follow-up. The ACT+SSRI condition demonstrated significant improvement in psychological flexibility, mindfulness, and valued living that were maintained at follow-up compared to the CBT+SSRI and continued SSRI conditions. Findings indicate that ACT+SSRI is comparably effective as CBT+SSRI at treating adolescent OCD. However, ACT+SSRI appears to differ from CBT+SSRI on changes in psychological flexibility, mindfulness, and valued living, indicating potential differences in mechanism of change.