We previously found that T cell immunoglobulin and mucin domain protein 3 (Tim-3) signaling contributed to intestinal homeostasis while the underlying mechanisms remain unclear.Here we demonstrate that Tim-3 signaling determines intestinal homeostasis and diseases by regulating macrophage polarization.The decreased Tim-3 expression in ulcerative colitis (UC) leads to a pathogenic pro-inflammatory macrophage response (M1),while the increased Tim-3 expression in colitis associated cancer (CAC) is closely related to an immunosuppressive anti-inflammatory macrophage response (M2).Tim-3 signaling regulates macrophage polarization in vitro.Intervention of Tim-3 pathway in ulcerative colitis and in colon cancer significantly attenuated diseases progression respectively by reversing the activity of macrophage.Tim-3 signaling promotes M2 macrophage polarization by inhibiting the expression of miR-155 and the phosphorylation of STAT1,two molecules which could form a positive feedback loop to promote the inflammatory response of macrophage.Tim-3 signaling also promotes the activity of SOCS1 and CEBP/b in macrophages; both of which are targets of miR-155 and are actively involved in the negative regulation of inflammatory responses.Further investigation on the physiopathological roles of Tim-3 in intestinal homeostasis will shed new light on the pathogenesis of intestinal diseases and find new therapeutic targets.