Ulcerative colitis (UC) develops through a complicated interaction between the host and microbiota. Intestinal fibroblasts are believed to play crucial roles in the pathogenesis of UC, but the influence of the host-microbiota interaction on the pathophysiology of intestinal fibroblasts remains poorly understood. Here, we demonstrate that OTU deubiquitinase 3 (OTUD3) suppresses pathologic activation of fibroblasts exposed to microbial cyclic GMP-AMP (3'3'-cGAMP) in the colon by deubiquitinating stimulator of interferon genes (STING). Mice harboring a UC risk missense variant in the Otud3 gene showed pathological features of UC in the colon after transplantation of a fecal microbiota with the potential to produce excessive cGAMP from patients with UC. Collectively, these results highlight a mechanism of the interaction between OTUD3 in host fibroblasts and STING-activating microbiota in UC development.