Clinical information and serum samples of 20 neuromyelitis patients and 30 patients with multiple sclerosis were collected in this study. The expression of anti-aquaporin 4 antibody in the serum of all patients was detected with an indirect immunofluorescence assay, using human embryonic kidney 293 cell line that stably express human-derived aquaporin 4 as a substrate. The characteristics of head and spinal magnetic resonance imaging were also observed in patients who had neuromyelitis and were positive for anti-aquaporin 4 antibody. Results showed that the expression of anti-aquaporin 4 antibody was significantly different between multiple sclerosis patients and neuromyelitis patients. There were 13 out of 20 neuromyelitis patients (including high-risk syndrome) that were positive for anti-aquaporin 4 antibody. The magnetic resonance imaging examinations of the head and spinal cord found that among the 13 positive patients, nine cases showed normal cerebral hemisphere and optic nerve, two cases had optic nerve changes, and one case had an atypical lesion in the brain. All 30 multiple sclerosis patients were negative for this antibody. The experimental findings indicate that patients with neuromyelitis optica had more than three lesioned segments in the spinal cord by magnetic resonance imaging, and the segment length of the injured spinal cord was not associated with the titer of aquaporin 4 antibody in neuromyelitis patients.