Spinal cord injury is one of the complications of the anterior cervical surgery. Motor weakness is occurred as a result of spinal cord injury and most of the motor weaknesses are accompanied by sensory deficit. We experienced a case of monoplegia of the lower extremity without sensory deficit after anterior cervical discectomy and fusion (ACDF). A 36-year-old male patient had multiple cervical disc protrusion at C4-5, 5-6 and 6-7. He had no neurologic deficit. Monoplegia was developed at the early postoperative period of ACDF. Reoperation was performed, but a definite spinal cord compression was not showed on operative field. We thought that spinal cord ischemia was the cause of monoplegia and was related to the operative posture of the hyperextension of the neck and poor blood supply to the spinal cord. A case of monoplegia without sensory deficit has not been reported. Therefore, we discuss the pathophysiology of monoplegia without sensory deficit.