Background: Although many experimental and clinical studies were performed on the pathophysiology and treatment of spinal cord injury (SCI), the electrophysiological and ultrastructural changes of the spinal cord were not precisely evaluated. Aims: To investigate the effect of mannitol on Somatosensory Evoked Potentials (SSEP), postoperative neurological recovery and ultrastructural findings after an experimental SCI. Setting: The experimental microsurgery laboratory of a university hospital. Design: A prospective, randomized animal study. Material and Methods: Sprague-Dawley rats were used and divided into three groups (Groups I-III) for this study. Those in Group I were control animals who underwent laminectomy only, and non-traumatized spinal cord samples were obtained 2 weeks later. SCI was produced in Groups II and III using clip compression technique, and cord samples were obtained 2 weeks later. The rats in Group 11 received 2 g/kg of 20% mannitol intraperitoneally, immediately and three hours after trauma was induced; and those in Group III received the same amount of 0,9% NaCl in the same manner. Preoperative and postoperative SSEP records at the end of 2 weeks were obtained. Electron microscopy examination of the cord samples was done at 2 weeks postoperatively. Statistical Analysis used: Fischer's Exact Test. Results: SSEP records, ultrastructural findings and clinical recovery showed that minor neural damage and significant recovery occurred in Group II. Conclusion: This study demonstrates that the administration of 2 g/kg of 20% mannitol produces significant improvement in the neural structures and protects the spinal cord following injury.