The thoracolumbar spinal cord receives its blood supply primarily from the artery of Adamkiewicz (AA), a branch of thoracolumbar intercostal arteries. Aortic cross-clamping during operation for descending aortic aneurysms can cause paraplegia due to spinal cord ischemia secondary to low blood flow through the AA. A 69-year-old woman was diagnosed with a left posterior mediastinal tumor measuring 66 mm. The tumor was adjacent to the thoracic aorta between Th10 to Th12 vertebral levels. Preoperative 3-dimensional computed tomography (3D-CT) imaging revealed 2 AAs originated from the 10th and 11th left intercostal arteries just near the tumor. The patient underwent a left thoracotomy and the 2 intercostal arteries were carefully dissected from the encapsulated tumor. Complete resection was safely achieved with preservation of the AAs. Pathology revealed a schwannoma. There were no complications. In performing thoracic surgery for posterior mediastinal tumors, it is important to identify the AAs preoperatively and preserve them.