The purposes of this study were to investigate the therapeutic effects of an early exercise program after mastectomy and to provide the early exercise program protocol for patients who had undergone mastectomy. The subjects were seventy women who were diagnosed with breast cancer. They were randomly as signed either to a experimental group (n=35) that received early postoperative exercise program or to a control group (n=35) that received only education by nurses. Data were obtained for each patient from goniometric measurements of shoulder flexion, abduction, external rotation, 10 elements of functional performance, and subjective pain evaluation using visual analogue scale (VAS). All variables were measured preoperatively, three days postoperatively, and one month postoperatively. Data were compared by groups using independent t-test and Mann-Whitney U test for parametric or non-parametric data, respectively. There were no significant differences between the groups for all variables preoperatively and at three days postoperatively. But there were significant differences at one month postoperatively. The experimental group showed a statistically significant increases in shoulder flexion, abduction, and external rotation and in the pain VAS at one month postoperatively (p<.05). Also, at one month postoperatively, the experimental group had less difficulty with three elements of functional performance-doing up a 'back' zippered article of clothing, reaching the ipsilateral scapula, and contralateral scapula with the fingers on the operated side-than the control group (p<.05). The results of this study suggest that, after mastectomy, the early exercise program conducted by a well-trained physical therapist can make a significant contribution to the return of more normal shoulder function and activities of daily living and to an increased quality of life.