Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune inflammatory neurological disease characterized by longitudinally extensive transverse myelitis (LETM) and optic neuritis. Interleukin (IL)-36 is a novel cytokine of the IL-1 family that is involved in the development of inflammatory diseases. The aim of this study was to investigate the role of IL-36α in NMOSD. We retrospectively collected 73 patients, who fulfilled the 2015 criteria for NMOSD diagnosis and were admitted to the Department of Neurology of the First Hospital of Jilin University from 2015 to 2016. Fifty age and gender matched patients with non-inflammatory neurological disorders (ONNDs) were collected in the same period and served as controls. Neurological function was evaluated by the expanded disability status scale (EDSS). All participants were assessed for the annual relapse rate (ARR). Blood and cerebrospinal fluid (CSF) samples were obtained and the levels of IL-36α in the serum and CSF were analyzed by enzyme-linked immunosorbent assay (ELISA). IL-36α levels in serum and CSF were found to be significantly increased in patients with NMOSD compared to those in the controls. Furthermore, IL-36α levels in both serum and CSF were positively correlated with the EDSS score. CSF IL-36α levels were positively correlated with CSF leukocyte counts, protein concentration and immunoglobulin IgG. Our results suggest that IL-36α may be a novel biomarker for monitoring disease severity in NMOSD.