BackgroundTo explore the gut microbiota characteristics in depressed patients with bipolar disorder (BD) as well as the connection between the gut microbiota and inflammatory markers.MethodsTotally 72 depressed BD patients and 16 healthy controls (HCs) were enrolled in the study. Blood and feces samples were taken from each subject. With the help of 16S-ribosomal RNA gene sequencing, the characteristics of the gut microbiota in each participant were examined. Correlation analysis was then utilized to assess the relationship between the gut microbiota and clinical parameters.ResultsWe found the taxonomic composition of the gut microbiota, but not its diversity, was significantly different in BD patients compared to HCs. We found the abundance ofBacilli,Lactobacillalesand genusVeillonellawere higher in BD patients than in HCs, while genusDoreawas more abundant in HCs. Additionally, correlation analysis showed that the bacterial genera’ abundance in BD patients was strongly correlated with the severity of depression and inflammatory markers.ConclusionsAccording to these results, the gut microbiota characteristics were changed in depressed BD patients, which may have been associated with the severity of depression and the inflammatory pathways.