Physical inactivity in patients with coronary artery disease is linked to recurrent cardiac events. Given that social support may be an enduring major factor for physical activity, the mechanism underlying the multiple mediating effects of self-efficacy and autonomous motivation on the relationship between social support and physical activity in patients with coronary artery disease has hardly been examined. Therefore, this study aimed to clarify the multiple mediating roles of social support and physical activity on the relationship between self-efficacy and autonomous motivation in patients with coronary artery disease. This descriptive cross-sectional study included 190 inpatients who were diagnosed with coronary artery disease and admitted to a cardiology ward university hospital in Korea. Parallel multiple mediated models were tested using the SPSS PROCESS macro. The direct effects of social support on physical activity and the indirect effects of self-efficacy and autonomous motivation on social support and physical activity were statistically significant. Thus, positive social support from health-care providers has an important role to play in promoting physical activity by increasing self-efficacy and autonomous motivation for physical activity in patients with coronary artery disease.