A 68-year-old man was scheduled for mediastinal tumor resection. Aortic invasion was unclear on preoperative computed tomography. Transesophageal echocardiography showed a smooth endothelial border, but the tumor was contiguous with the distal arch, and the adventitial border was unclear. After median sternotomy, the tumor was found to be adherent to the aorta. An endovascular stent graft was placed in the distal arch to protect the aorta, but excessive bleeding occurred from the aortic defect on tumor removal. This case shows that massive hemorrhage can occur during the resection of an aorta-invading tumor despite the use of an endovascular stent graft.