The aim of this study was to investigate the effectiveness of positive psychology-based psychotherapy in enhancing resilience, cognitive flexibility, and cognitive-emotional regulation in adolescents from underprivileged areas. Materials and Methods: This study was applied in terms of its goal and experimental in terms of data collection method, using a pre-test-post-test-follow-up design. The statistical population of this study consisted of adolescents from underprivileged areas. The sample was selected through accessible sampling from the target population, consisting of 30 individuals who were then divided into two groups: an experimental group (15 participants) and a control group (15 participants). The research tools included the Connor-Davidson Resilience Scale (CD-RISC), the Dennis and Vander Wal Cognitive Flexibility Questionnaire (DFQ), the Cognitive-Emotional Regulation Questionnaire (CERQ), and a protocol for positive psychology-based psychotherapy. Findings: The results of analysis of covariance showed that positive psychotherapy significantly affected the scores for resilience, cognitive flexibility, and cognitive-emotional regulation at the post-test stage, and this effect remained stable at the follow-up stage. The effect size of this treatment explained 45.72%, 49.85%, and 48.16% of the variance in the scores, respectively. These results indicate the effectiveness and sustainability of positive psychotherapy on these three variables. Discussion and Conclusion: Overall, the results indicated that positive psychology-based psychotherapy had a positive and significant impact on cognitive-emotional regulation, cognitive flexibility, and resilience in adolescents from underprivileged areas.