This study examines the effects of a rehabilitation program on quality of life (QOL), cardiopulmonary function and fatigue during radiotherapy for breast cancer patients. The program includes aerobic exercise, stretching and strengthening exercises. Sixty-five women participated in this study and they were asked to perform supervised exercises that last for 60 minutes five times a week for six weeks. The European organization for research and treatment of cancer-cancer (EORTC QLQ-C30) and the breast (EORTC QLQ-BR23), predicted maximal volume of oxygen consumption ($VO_{2max}$) and fatigue severity scale (FSS) were assessed before and after the rehabilitation program. The 60-minute program consisted of a 10-minute warm-up, 30-minute of aerobic exercises, and 15-minute of strengthening exercises, followed by a five-minute cool-down. Heart rates were monitored throughout the exercise class to ensure that patients were exercising at the target heart rate of 40~75% of the age-adjusted heart rate maximum. There were statistically significant differences in the changes of physical function and cancer related symptoms in the EORTC QLQ-C30 and EORTC QLQ-BR23 (p<.05). There was a statistically significant improvement in the predicted $VO_{2max}$ (p<.05), although there were no significant differences in the FSS (p>.05). The results of our study suggest that a supervised rehabilitation program may benefit the physical aspects and QOL of patients receiving radiotherapy for breast cancer.