Updated project metadata. Healthy human and mouse colon epithelium is a major source of active thrombin, released in lumen. Using germ-free animals, we demonstrated that mucosal thrombin was directly regulated by the presence of commensal microbiota. Specific inhibition of lumenal thrombin activity caused macro-, microscopic damage and transcriptomic alterations of genes involved in host-microbiota interactions. Further, lumenal thrombin inhibition impaired the spatial segregation of microbiota biofilms, allowing bacteria to invade the mucus layer and to translocate across the epithelium. Thrombin proteolyzed the biofilm matrix of reconstituted mucosa-associated human microbiota. We demonstrated a previously unknown physiological role for epithelial thrombin that constrains biofilms at mucosal surfaces. We report that lung, bladder and skin epithelia also expressed thrombin, suggesting that this role may be applicable to other host-microbiome surfaces. Our discovery points route to new therapies targeting biofilms, important for a broad range of disorders, in the gut, and beyond.