A 20-year-old man with a posterior mediastinal tumor incidentally found on a chest X-ray was referred to our hospital. Chest computed tomography showed a 3 cm nodule located on the left side of the 10-11th thoracic vertebra, where the artery of Adamkiewicz is presumed to arise. He underwent left thoracotomy to remove the lesion. The tumor was safely resected with the assistance of intraoperative motor evoked potential(MEP) monitoring. The postoperative diagnosis was a benign schwannoma. In thoracic surgery for posterior mediastinal tumors, intraoperative MEP monitoring is useful for preventing paraplegia.