A 77-year-old woman was admitted to the hospital for heart failure with orthopnea. Echocardiography revealed massive mitral regurgitation. During preoperative cardiac catheterization, an aneurysm was indentified incidentally just below the tracheal carina. Three dimensional computed tomography showed three bronchial artery aneurysms behind the pulmonary artery and the left atrium. The proximal aneurysm was the largest and was 22 mm in diameter. It was resected by retracting the ascending aorta to the left, the superior vana cava to the right and right pulmonary artery cranially under cardiopulmonary bypass, and mitral valve plasty was performed. We believed that resection of the proximal aneurysm would cause thrombotic occlusion of the other 2 aneurysms. Bronchial artery aneurysm is a rare entity that is observed in fewer than 1% of those who undergo selective bronchial arteriography. In addition, because bronchial artery aneurysm is a potentially life-threatening lesion, it should be treated promptly when diagnosed.