IIntroduction: Breast cancer is the most common type of cancer among women, and according to the report of the World Health Organization, this statistic has been increasing in recent years, so the present study aim was to compare the effectiveness of group positive behavioral therapy and group cognitive-behavioral therapy on Cognitive Flexibility among women with breast cancer. Methods: The present study was an experimental study.The selected statistical population of the study included all women with breast cancer who referred to the breast clinic of Milad Hospital in 1400. Among the clients, 45 people were selected by random face sampling. People were randomly divided into two experimental groups and one control group (15 people). The experimental groups underwent cognitive-behavioral and positive therapy in 8 weekly sessions of 90 minutes. Dennis and Vanderwaal's cognitive flexibility questionnaire was used to collect information. The data was analyzed using multivariate covariance analysis with SPSS-20 software. Findings: The results indicated a significant difference between the effects of the two treatments on the variable scores of cognitive flexibility (F = 65.134 and 0.000 (P < 0.000). Cognitive behavioral therapy group had a greater effect on the cognitive flexibility of women with breast cancer compared to the positive treatment group, but positive treatment group on all three components of perception of different options (F=83.446 and P<0.000), controllability perception (F=430.20 and 0.000 (P<0.00) and perception of behavior justification (F=38.128 and 0.000) 000 (P<) was effective. Conclusion: The findings of this study showed that the use of cognitive behavioral therapy and positive behavioral therapy can improve the cognitive flexibility of women with breast cancer, so the use of these methods is recommended by counselors and psychologists in clinics and hospitals.