Although ursodeoxycholic acid (UDCA) has long been used for patients with chronic cholestatic liver diseases, particularly primary biliary cirrhosis, it may modulate the host immune response. This study investigated the effect of UDCA feeding on experimental hepatitis, endotoxin shock, and bacterial infection in mice. C57BL/6 mice were fed a diet supplemented with or without 0.3% (w/v) UDCA for four weeks. UDCA improved hepatocyte injury and survival in concanavalin-A (Con-A)-induced hepatitis by suppressing IFN- production by liver mononuclear cells (MNC), especially NK and NKT cells. UDCA also increased survival after lipopolysaccharide (LPS)-challenge; however, it decreased survival of mice following Escherichia coli (E. coli) infection due to the worsening of infection. UDCA-fed mice showed suppressed serum IL-18 levels and production of IL-18 from liver Kupffer cells, which together with IL-12 potently induces IFN- production. However, unlike normal mice, exogenous IL-18 pretreatment did not increase the serum IFN- levels after E. coli, LPS or Con-A challenge in the UDCA-fed mice. Interestingly, however, glucocorticoid receptor (GR) expression was significantly upregulated in the liver MNC of the UDCA-fed mice but not in their whole liver tissue homogenates. Silencing GR in the liver MNC abrogated the suppressive effect of UDCA on LPS- or Con-A-induced IFN- production. Furthermore, RU486, a GR antagonist, restored the serum IFN- level in UDCA-fed mice after E. coli, LPS or Con-A challenge. Taken together, these results suggest that IFN--reducing immunomodulatory property of UDCA is mediated by elevated GR in the liver lymphocytes in an IL-12/18 independent manner.