Pseudoaneurysm of the thoracic aorta is a rare condition and usually occurs following blunt trauma. It is almost fatal in the absence of prompt surgical treatment. We describe the case of a 56-year-old male suffering from intermittent nonmassive hemoptysis, mild dysphagia, and atypic chest pain for 1 month who has no history of trauma. A saccular aneurysm at the aortic arch between left common carotid artery and left subclavian artery was diagnosed by magnetic resonance imaging. Intraoperatively, compression of surrounding structures including trachea and esophagus by the aneurysmal sac (6 x 8 cm in diameter) was seen. Pseudoaneurysm adherent to the upper lobe of the left lung was resected and entire aortic arch replacement with a prosthetic graft was performed. Postoperative course was uneventful and neither specific changes on histologic examination nor any evidence of infection could be detected.