Breast cancer is one of the most common diseases among women, and regular exercise has positive effects on slowing the progression of this disease. Therefore, in order to investigate the mechanisms involved, the present study randomly divided 36 eligible postmenopausal women with breast cancer into two exercise and control groups. After filling out the consent form and familiarizing themselves with the exercise protocol, baseline blood samples were taken from all subjects. Then, the exercise group performed Dragon Boat exercises three days a week for 12 weeks at an intensity of 65 to 85% of maximum heart rate, and the control group continued their normal lives. Finally, 48 hours after the last training session, a second sample was taken from all subjects and sent to the laboratory to examine changes in P53 gene expression using ELISA. Independent t-test and paired t-test were also used to analyze the data. The data results showed that Dragon Boat training significantly increased P53 levels compared to the control group (p=0.042). P53 is one of the most important genes involved in tumor growth suppression, apoptosis, and DNA repair. As a result, it seems that one of the mechanisms of the effect of exercise training in slowing the progression of breast cancer in postmenopausal women is the increase in the expression of the P53 gene, which suppresses tumor growth.