Purpose: The study was conducted to find out clinical characteristics for coronary artery disease patients with diabetes mellitus. Methods: We retrospectively reviewed the electronic medical records which included the data of 6,792 patients, who had been diagnosed coronary artery disease (CAD) such as angina or acute myocardial infarction and admitted to a university hospital in Seoul from January, 2005 to November, 2010. Results: Of the 6,792 patients, 43% had been diagnosed diabetes as comorbidity. The CAD patients with diabetes had lower left ventricular ejection fraction, stayed longer at hospital, and spent on more time from the first symptom to hospital visit than those without diabetes. In addition, they were more likely to have multi vessel coronary artery disease. Conclusion: The CAD patients with diabetes lay on the various factors which can make more worsen condition. Hence, we need to pay attention to specialized nursing care and patient education for the CAD patients with diabetes.