We report the case of a large vein graft aneurysm that occurred 15 years after a coronary artery bypass, after which we successfully performed a re-bypass. A 57-year-old woman had four coronary bypasses using a great saphenous vein and two internal mammary arteries. An abnormal shadow was incidentally noted on a chest radiograph and diagnosed as a great saphenous vein aneurysm. Preoperative inspection found that the only available graft for re-bypass was the small saphenous vein. The bypass to the right coronary artery was performed using an off pump technique and the aneurysmal graft was removed. She was discharged without any problems after the operation. The pathological examination showed arteriosclerotic changes most likely caused by risk factors such as long-term use of steroids to treat systemic lupus erythematosus, chronic dialysis, and smoking.