Thoracic graft infection is a serious complication and has high mortality. We report a case of successful treatment of graft infection after ascending thoracic aortic reconstruction. A 66-year-old woman underwent surgery for DeBakey type I aortic dissection in June 2007. The ascending aorta was replaced with a prosthetic graft. Although her postoperative course was complicated with Methicillin-resistant Staphylococcus aureus (MRSA) mediastinitis, the infection was conservatively controlled by mediastinal lavage and antibiotics. However, she was readmitted in April 2008 due to lumbar pain and high fever, and was diagnosed with infectious spondylitis. Lumbar plastic surgery was performed. During hospitalization, she underwent total systemic examination. The results indicated aneurysm of the ascending aorta. MRSA was detected from culture fluid of her blood. Taken together, the presence of an infected aortic aneurysm was considered possible. Consequently, reconstruction of the ascending aorta using two allografts was performed after removing the prosthetic graft. The postoperative course was uneventful, and she was discharged on the 71st postoperative day. The patient continues to thrive 9 months after the operation. This case of an infected aortic aneurysm repaired with the use of allografts will be reported together with references to the literature.