Abstract Inflammatory bowel disorders (IBD) including ulcerative colitis (UC) and Crohn’s disease (CD) affect between 1–3 million people in the United States with prevalence on the rise. Patients present with symptoms including diarrhea, abdominal cramps, and weight loss. Many factors are implicated in pathogenesis, including host immune response. Identification of molecules that regulate IBD is critical in understanding pathogenesis. ST8Sia6 is a sialic acid transferase that adds terminal a2,8 disialic acids to cell surface glycoproteins, and we have found that ST8Sia6 knockout (KO) mice exhibit increased spontaneous small bowel lamina propria CD4 TH1 polarization, increased inflammatory cytokine production, and decreased IgA class switching of Peyer’s patch B cells, indicative of inflammation. Additionally, adult ST8Sia6 KO mice have shortened small bowels, likely due to baseline inflammation. These mice do not exhibit obvious baseline symptoms, but ST8Sia6 KO mice exhibit increased weight loss and decreased survival when challenged with dextran sodium sulfate (DSS)-induced colitis, which was also enhanced when co-housed with wildtype (WT) mice and after antibiotic treatment. These DSS-challenged ST8Sia6 KO mice exhibit increased histological damage and immune infiltration of the gut as compared to WT controls. The accelerated DSS-colitis is also observed when ST8Sia6-deficient bone marrow is transplanted into WT recipients, indicating that the effect is mediated specifically by immune cells. This data demonstrates a role for ST8Sia6 in regulating the host immune response to inflammatory bowel disorders, and further elucidating this role will aid in developing a mechanistic understanding of IBD pathogenesis. Supported by grants from NIH R01 CA243545