Background: Lack of physical activity has been noted in breast cancer survivors and been attributed to decreased physical function. Purpose: This study assessed the effects of a moderate-to-vigorous physical exercise program on body fat percentage, maximal oxygen consumption (VO[subscript 2] max), body mass index, and bone mineral density (BMD) of breast cancer survivors. Methods: Eleven stage I and II breast cancer patients, 40-65 years old, were recruited to assess VO[subscript 2] max, BMD, weight, and percentage of body fat before and after an 8-week exercise (aerobic and resistance training) intervention. Results: Supervised exercise significantly improved aerobic capacity (+4.227 ml/kg/min; P=0.004) and increased, though not significantly, bone mass densities of hip (+0.433 SD units; P=0.061) and spine (+0.224 SD units; P=0.350). No significant changes were observed for body mass index (+0.0196 kg/m[superscript 2]; P=0.927) or body fat percentage (-0.737%; P=0.639). Discussion: Understanding how breast cancer survivors tolerate and respond to a moderate-to-vigorous exercise program is an important step in developing programs for this population following recovery. Translation to Health Education Practice: Moderate-to-vigorous physical exercise may be an effective and well-tolerated intervention for improving physical function in breast cancer survivors. (Contains 2 tables and 3 figures.)