The protective action of ursodeoxycholic acid (UDCA) in cholestatic liver diseases may be mediated by choleresis, detoxification and cytoprotection against oxidative stress. Nrf2, one transcription factor, serves as a cellular stress sensor and is a key regulator for hepatic induction of detoxifying enzymes, antioxidative stress genes and numerous Mrp family members. We aimed to investigate whether UDCA induces hepatic Mrp expression along with that of detoxifying enzymes and antioxidative stress genes via the Nrf2 transcriptional pathway. The protein level, subcellular localization and mRNA level of Mrp family members were assessed in livers of Keap1 gene-knockdown (Keap1-kd) mice and those of UDCA-fed WT and Nrf2 gene-null (Nrf2-null) mice. Nuclear levels of Nrf2 in livers of Keap1-kd mice markedly increased, resulting in constitutive activation of Nrf2. Keap1-kd mice have high-level expression of hepatic Mrp2, Mrp3 and Mrp4 relative to WT mice. UDCA caused potent Nrf2 nuclear translocation (activation) in mouse livers, and the treatment of WT and Nrf2-null mice showed maximal hepatic induction of Mrp2, Mrp3 and Mrp4 in association with enhanced membranous localizations in an Nrf2-dependent manner. UDCA similarly caused Nrf2 nuclear translocation, and chromatin immunoprecipitation assays revealed the binding of Nrf2 to antioxidant response elements in the promoter regions of Mrp2, Mrp3 and Mrp4. These findings demonstrate an essential role of Nrf2 in the induction of Mrp family members in livers, and suggest that a therapeutic mechanism of UDCA action is, via Nrf2 activation, a stimulation of detoxification and antioxidative stress systems, along with Mrp-mediated efflux transport.