Background: Accumulating evidence points to an association of alternations in the gut microbiota with health and disease, including the development of neurological diseases. However, there are relatively scarce studies of the role of the gut microbiota in neuromyelitis optica spectrum disorders (NMOSD). Therefore, the aim of the present study was to evaluate the differences in the intestinal microbiota composition between patients with NMOSD and healthy control subjects. Methods: This was a cross-sectional study. Stool samples were obtained from 20 patients with NMOSD and 20 healthy family members of the patients as controls (HC). The bacterial 16S rRNA gene amplification sequencing (V3-V4 region) was used to detect the composition and structure of the intestinal microbiota community in the two groups. Results: The gut microbiota compositions clearly differed between the NMOSD and HC groups, although there was no significant difference in the overall microbial community structure. In detail, patients with NMOSD had an increased abundance of the pathogenic genera Flavonifractor (P = .004) and Streptococcus (P = .007) compared with the HC. In addition, several intestinal commensal bacteria were detected at significantly lower abundance in the NMOSD patients compared to the controls, including Faecalibacteriurn, Lachnospiracea_incertae_sedis, Prevotella, Blautia, Roseburia, Romboutsia, Coprococcus, and Fusicatenibacter (all P < .05). ROC curve analysis suggested that gut microbiota genera had potential to distinguish NMOSD from controls. Functional analysis further indicated that the gut microbiome of NMOSD patients was associated with three significantly downregulated metabolic pathways: "Photosynthesis" (P < .001), "Photosynthesis proteins" (P < .001), and "Thiamine metabolism" (P = .007). These differences remained significant even after correction for multiple comparisons (all PFDR < 0.05). Conclusion: Our results reveal the dysbiosis of intestinal bacteria and regarding metabolic abnormalities in patients with NMOSD. Further studies are warranted to elucidate the potential mechanism by which dysbiosis of microbiota contributes to the onset and progression of NMOSD.