and Purpose: Obsessive-compulsive disorder in children and adolescents not only affects their cognitive, social and educational functions, but also affects the family system of these individuals. Therefore, the purpose of this study was to investigate the effect of acceptance and commitment therapy on the psychological flexibility of children with obsessive-compulsive disorder. Method: In this study, a single case method with A-B design was used. Four children aged 7-12 years were selected

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... purposeful sampling. The children's obsessive compulsive disorder questionnaire (Goodman et.al, 1986) and avoidance and fusion questionnaire (Grigo et.al, 2005) were used to collect data. After the 4 sessions of the baseline, the participants received 9 sessions of acceptance and commitment treatment, the first 3 sessions were for their parents. The follow-up test was performed 40 days after treatment. The findings of this study were analyzed based on visual analysis and descriptive statistics indexes. Results: Based on the visual analysis of the data chart, acceptance and commitment treatment was effective for all four subjects (percentage of non-overlap of points of two experimental situations of base line and intervention 775%, 75%, 100% and 75% for subjects 1, 2, 3, and 4. Conclusion: The results of the study indicated the beneficial effects of acceptance and commitment therapy on the psychological flexibility of children with obsessive-compulsive disorder, which can be used to increase the psychological health of these children.