Background & Objective: To evaluate the prevalence of aquaporin-4 antibody (AQP-4 Ab) seropositive patients in neuromyelitis optica (NMO) and neuromyelitis optica spectrum disorder (NMOSD) and to compare the clinical, investigation features and treatment outcome between the AQP-4 Ab seronegative and seropositive groups. Methods: All NMO and NMOSD patients in Maharat Nakhon Ratchasima hospital during January 2012 to December 2016 were recruited. Demographic, clinical, laboratory and imaging data were collected from the medical records. All data were analysed and compared between seropositive and seronegative groups as appropriates. Results: There were 12 (29%) and 30 (71%) NMO and NMOSD patients, respectively. There were 30 (71%) patients who hadAQP-4 Ab seropositive status. Thirty-three (78.6%) patients were female. In seropositive group, there were significantly higher proportion of female patients (87% versus 58%, p=0.04), immunosuppressant treatment (33% versus 0%, p=0.04), patients who had serum albumin less than 4 g/dL (46% versus 0%, p=0.02), cerebrospinal fluid (CSF) pleocytosis (71% versus 17%, p=0.01) and patients with extensive spinal cord involvement (67% versus 25%, p<0.05) than seronegative group. CSF-serum glucose ratio was significantly lower in seropositive group than seronegative group (0.5 + 0.03 versus 0.7 + 0.04, p=0.01). Conclusion: The prevalence of AQP-4 Ab seropositive patients in NMO and NMOSD was 71%. There were significantly more female patients, immunosuppressant treatment, patients with serum albumin less than 4 g/dL, CSF pleocytosis, low CSF-serum glucose ratio and extensive transverse myelitis than seronegative group.