A coronary artery aneurysm was first reported by Bougon in 1812, and was able to be diagnosed during life with advance of selective coronary arteriography. We have recently seen a 62-year-old woman who had intermittent anterior chest pain and dyspnea on exertion(NYHA functional class II) and diagnosed a coronary artery aneurysm by coronary arteriography. A saccular formed coronary artery aneurysm was located at left main coronary artery at the juction of the bifurcation of LAD and left circumflex artery and it's was 2cm×2cm and it's thickness of wall was 0.5cm. After the patency and consistency of coronary arteries were confirmed,resection of aneurysm with aneurysmorrhaphy was performed.