Spontaneous spinal subarachnoid hemorrhage occurs less than 1% of all cases of subarachnoid hemorrhage or hematoma. The causes of spinal subarachnoid hemorrhage or hematoma, include trauma(often caused by lumbar puncture), vascular lesions, neoplastic lesions, coagulopathy, hypertension and Behcet's disease. The occurrence of spontaneous spinal subarachnoid hematoma of unknown pathogenesis is extremely rare. We report a case of spontaneous spinal subarachnoid hematoma of unknown origin at thoracic level of a 33-year-old woman. At admission, she presented with back pain and paraparesis for 3 days prior to admission. There was no history of trauma and use of anticoagulants. On thoracic CT, the lunate shaped high density mass which displaced the spinal cord to right side at T3 to T6 was showed, but did not show contrast enhancement. On thoracic MRI, this mass was iso-signal intensity in T1 weighted image and low-signal intensity in T2 weighted image. In GDTA-enhanced MRI, the mass was not enhanced. We removed subarachnoid hematoma with total laminectomy through T4 to T6. Her neurologic deficit was fully improved and discharged. We conclude that even if the rate of spontaneous spinal subarachnoid hematoma of unknown is low, the clinical symptom may progress rapidly. Therefore, early diagnosis and removal of hematoma is essential for improvement of the patient's neurologic deficit. inhibition of vestibular nuclear complex through nhibitory Purkinje system.