Background and Aims: Given the success of group psychotherapy as well as drug therapies to improve drug-dependent patients, it is increasingly necessary to compare different interventions to select the most effective way to reduce the problems of methadone maintenance therapists. This study aimed to compare the effectiveness of existential group therapy with cognitive-behavioral group therapy on increasing the life satisfaction of addicted people under methadone maintenance therapy. Materials and Methods: This semi-experimental study was conducted based on the pretest-posttest method with a control group. The study population included addicted males who underwent methadone maintenance treatment at Qazvin Addiction Treatment and Injury Clinics in 2019, Qazvin, Iran. The participants (n=90) were randomly selected and divided into experimental (existential and cognitive-behavioral therapy) and control groups. Subsequently, the experimental groups participated in 10 sessions of 120-min per week. The data were analyzed in SPSS software (version 22) through a repeated-measures ANOVA. Results: The results showed the improvement of life satisfaction in the existential and cognitive-behavioral therapy groups (P<0.001); however, the control group showed no significant difference in pretest, posttest, and follow-up. Furthermore, the results indicated no significant difference between cognitive-behavioral and existential therapy groups in terms of life satisfaction (P>0.05). Conclusion: It can be concluded that both cognitive-behavioral and existential therapies are effective in increasing the life satisfaction of addicted patients under methadone maintenance therapy; however, no significant difference was observed between the two experimental groups regarding the increasing level of satisfaction.