Ulcerative colitis (UC) remission is marked by gut microbiota restructuring, but how microbial metabolites influence immune-mediated tissue repair is unclear. Here, we demonstrate that oral vancomycin alleviates colitis symptoms in murine models, mirroring its clinical efficacy in inducing remission in patients with UC. Mechanistically, vancomycin’s therapeutic effect is achieved by reducing deoxycholic acid (DCA). We reveal that DCA impairs mucosal repair driven by group 2 innate lymphoid cells (ILC2s) by inducing ER stress through direct binding to thioredoxin-related transmembrane protein 2 (TMX2). This interaction disrupts TMX2’s role in protein folding, triggering unresolved unfolded protein response via hyperactivation of PERK/eIF2α signaling, which suppresses the production of pro-healing molecules by ILC2s. Pharmacological inhibition of PERK phosphorylation restores ILC2 function and accelerates colitis resolution. Our work uncovers a pathogenic microbiota/DCA/ILC2 axis that obstructs mucosal healing and positions vancomycin as a targeted strategy to eliminate DCA, thereby promoting UC remission.