Post-thoracotomy paraplegia after non-aortic surgery is an extremely uncommon complication. A 56-year-old woman presented with a 1-year history of progressive shortness of breath. Computed tomography revealed a locally advanced posterior mediastinal mass involving the ribs and the left neural foramina. Tumor excision with a left pneumonectomy was performed. Post-resection, bleeding was noted in the vicinity of the T4-T5 vertebral body, and the bleeding point was packed with oxidized cellulose gauze (Surgicel®). Postoperatively, the patient complained of bilateral leg numbness extending up to the T5 level, with bilateral paraplegia. An urgent laminectomy was performed, and we noted that the spinal cord was compressed by two masses of Surgicel® with blood clots measuring 1.5 × 1.5cm at T4 and T5 levels. The paraplegia did not improve despite the removal of the mass, sufficient decompression, and aggressive postoperative physiotherapy. Surgeons operating in fields close to the intervertebral foramen should be aware of the possible threat to the adjacent spinal canal as helpful hemostatic agents can become a preventable threat.