Purpose: The purpose of this study was to investigate the effects of an exercise program on physical function and quality of life of mastectomy patients. Method: This study was conducted from October, 2004 to June, 2005. The subjects consisted of 60 patients with breast cancer(30 each in the experimental and control groups). The subjects in the experimental group participated in an exercise program for 16 weeks. Evaluation was performed four times in both the experimental and control group. Results: The results revealed an increase in physical function in the experimental group including wrist circumstance, function of shoulder joint, stretching, and upper endurance. Also, an increase in function scales in quality of life were significantly higher in the experimental group than the control group. In addition subjective comments on how they felt after participating in the exercise program were good in the experimental group. Conclusion: The 16-week exercise program showed a large positive effect on physical function and quality of life of breast cancer patients after a mastectomy.