The purpose of this study was to explore maximal oxygen uptake (VO2 max), fitness self-efficacy, and quality of life (QOL), and to examine the impact of VO2 max and fitness self-efficacy on QOL, among coronary artery bypass graft (CABG) patients. A total of 47 subjects who met the selection criteria were selected from a medical center. A graded exercise test was performed to estimate each subject’s VO2 max. Fitness self-efficacy and QOL were measured by the 18-item Fitness Self-Efficacy Scale and the SF-36, respectively. The results of the study revealed that the average VO2 max was 5.48 mets. A subjects’ fitness self-efficacy was medium low and QOL was medium high. The average score in the physical dimension of QOL was significantly lower than in the mental health dimension. Age was a significant predictor of fitness self-efficacy, and both age and body mass index were significant predictors of VO2 max. However, fitness self-efficacy was a more dominant predictor of QOL than was VO2 max. These findings may provide some directions in improving QOL in CABG patients.