Pulmonary artery aneurysm is a rare lesion of the thoracic cavity. Different etiologies have been reviewed, but idiopathic lesions without other symptoms are seldom reported. Usually, surgical interventions are suggested, but the long-term outcomes are not well established. Here, we report a 24-year-old man with main pulmonary artery aneurysm who successfully underwent aneurysmectomy and polytetrafluoroethylene vascular graft replacement. The postoperative course was uneventful, and the following image study revealed normal size of the great vessels.