Malnutrition impairs quality of life and prognosis of patients with cardiovascular disease. The Mini Nutritional Assessment (MNA) is a screening tool developed for the nutritional assessment of older adults. However, usefulness of MNA for patients undergoing cardiac rehabilitation (CR) has not been fully investigated.From March 2017 to September 2019, the MNA-short form (MNA-SF) and the MNA total score in patients undergoing phase II CR at the Juntendo University Hospital were evaluated.A total of 336 patients (mean age 70.1 ± 11.4 years; males: 209) were analyzed. In the MNA-SF, 157 patients (47%) were found to be malnourished or at risk of malnutrition. In MNA total score, 168 patients (50%) were found to be malnourished or at risk of malnutrition. The MNA-SF < 12 group had significantly lower body mass index (BMI), hemoglobin level, low MNA scores for protein/water intake, self-evaluation of nutrition and health, and upper arm and calf circumferences compared to the MNA-SF ≥ 12 group. Assuming BMI < 18.5 as malnutrition, the sensitivity and specificity for malnutrition were 100% and 58.9% for MNA-SF, and 96.9% and 54.9% for MNA total score, respectively.MNA is useful in screening for malnutrition in patients undergoing CR. Approximately 50% of them were determined to be malnourished or at risk of malnutrition, suggesting the need for detailed evaluation regarding their food intake and dietary intervention.