We conducted a randomized, controlled trial to evaluate the effect of self-monitoring approach (SMA) on exercise maintenance, self-efficacy for physical activity (SEPA), and objective physical activity (OPA) over the long-term after supervised cardiac rehabilitation (CR). Forty-five myocardial infarction (MI) patients (mean age 64.2 years) were recruited following completion of an acute-phase exercise-based CR program. Patients were randomly assigned to a SMA or control group. Along with CR, the SMA group performed self-monitoring of their weight and OPA for 6-months ; the control group participated in CR only. Twelve months after MI onset, exercise maintenance, SEPA scores, and OPA as a caloric expenditure were assessed. More patients maintained their exercise routine in the SMA than the control group. Mean SEPA score and mean OPA after CR were significantly higher in the SMA than control group. SMA during CR may effectively increase exercise maintenance, SEPA, and OPA over a 1-year after MI.