Background: Nowadays, regarding to spread drug addiction in society, high cost for the treatment of addicts and returning them to normal life is spent. This can only be possible with modern and effective ways. The present study has been conducted to determine the effectiveness of cognitive - behavioral therapy on psychological well-being of patients treated with methadone. Materials and Methods: This is a quasi-experimental case control study. Participants included 60 patients undergoing methadone treatment in both private drug rehabilitation center in Zirkouh and harm reduction center of Zirkouh. The subjects were randomly assigned to two experimental groups (n = 30) and control (n = 30).The experimental group received 12 sessions of cognitive-behavioral in Carol style and the control group only received methadone. All subject completed the psychological well-being questionnaire before and after intervention Results: The results showed that cognitive behavioral psychological well-being (pre: 27.66 ± 161/8 test: 24/04 ± 202/71) of patients undergoing methadone treatment had a positive effect (f=4.293, p<0.05). MANCOVA analysis results revealed that cognitive behavioral therapy has a positive impact on psychological well-being components of people who were addicted treated by methadone (f=12.80, P<0.01). Investigating the psychological well-being the results showed that there was no statistical significant relationship between personal development components among the two groups. Conclusion: Cognitive - behavioral therapy is effective in improving psychological well-being of patients undergoing methadone treatment. Therefore, it is recommended that in addition to pharmacological interventions, the cognitive-behavioral approach can be used to improve and accelerate the treatment course.