2Introduction: Methadone users face psychological challenges that require training to support their treatment. Objective: This study aimed to compare the effectiveness of mindfulness group training and cognitive-behavioral Therapy (CBT) groups in enhancing resilience and self-efficacy among individuals undergoing methadone treatment. Material and Methods: This study used a quasi-experimental design with pre-test, post-test, control groups, and a follow-up phase. The research population included 2, 500 individuals under the welfare organization’s supervision, receiving methadone treatment at addiction treatment centers in two Tehran cities in the second half of 2018. A total of 45 participants were chosen using convenience sampling, then randomly assigned to mindfulness, CBT, and control groups (15 people per group). Mindfulness training comprised eight 60-minute sessions, while CBT involved weekly 90-minute sessions for the experimental groups, the control group received no intervention. Participants completed the General Self-Efficacy Scale (Scherer & Maddox) and the Connor-Davidson Resilience Scale at pre-test, post-test, and one month post-treatment. Data were analyzed using two-way repeated measures ANOVA and Bonferroni post hoc tests, with a significance level of 0. 05. Results: The findings revealed that, post-intervention, the average resilience score in the mindfulness training group rose to 100. 85±8. 1, with self-efficacy also increasing to 66. 70±5. 20. In contrast, the CBT group showed an increase in resilience to 85. 95±13. 77 and in self-efficacy to 57. 85±7. 50 (P<0. 001). Compared to CBT, mindfulness group training demonstrated a more enduring effect over a one-month follow-up period (P<0. 005). Post-hoc tests confirmed that both interventions enhanced resilience and self-efficacy, with mindfulness training having a significantly greater impact (P<0. 001). Conclusion: The results confirmed that group mindfulness training and cognitive-behavioral group Therapy positively impact the resilience and self-efficacy of individuals undergoing methadone treatment. It is recommended that counselors and therapists use these two therapeutic approaches when working with individuals in methadone treatment.