Background: Anger rumination affects adolescents’ mental health and seriously damages their functions in interpersonal and communication situations and their social adjustment function in various family, academic and occupational situations. Objective: The present study aimed to investigate the relation of anger rumination and self-criticism with social maladjustment with the mediating role of psychological flexibility in adolescent boys and girls in Ahvaz (Iran). Materials & Methods: This descriptive cross-sectional study was conducted using Structural Equation Modeling (SEM). The statistical population was all secondary school students of Ahvaz in the 2020-21 academic year. The 848 participants (443 girls and 405 boys) aged between 16 and 18 years old, were selected using multistage cluster sampling. The research instruments included the Anger Rumination Scale, Levels of Self-Criticism Scale, Acceptance and Action Questionnaire–II, and Social Development Scale. Multigroup SEM was used to compare the proposed model between the girls and the boys. Results: There was a significant direct relationship between anger rumination, self-criticism, psychological flexibility, and social maladjustment (P<0.001). The findings suggested that psychological flexibility played a mediating role in the relationships of anger rumination and self-criticism with social maladjustment (P<0.01). In addition, there was a significant direct relationship between anger rumination and self-criticism to social maladjustment in boys, while this relationship was not significant in girls. Conclusion: The results suggested the desirable goodness of fit of the final model. Therefore, it is suggested to consider the roles of anger rumination, self-criticism, and psychological flexibility in predicting social maladjustment in students while regarding their gender differences in developing and implementing educational programs