A 74 year-old man visited our hospital complaining of increasing sensory disorder of the left lower extremity. On physical findings, a pulsatile mass was detected in abdomen, but he had been aware of it for 5 years. Further examination revealed on inferior mesenteric artery aneurysm 8 cm in diameter. It had no communication with other visceral arteries or veins. Surgical treatment was performed to resect the aneurysm without revascularization. The postoperative course was uneventful. The pathological examination of the aneurysm showed atherosclerotic change. The chief complaint on admission was unchanged following surgery and was thought to have no relation to the aneurysm. It was thought that to derive from lumbar vertebral disease. After operation, regular follow-up is necessary to check for pseudoaneurysms formation at the surgical margin and development of other visceral artery diseases.