We previously reported that Lgr4 has a critical role in the morphogenesis of kidney, but the detailed functions of Lgr4 in kidney development have not been elucidated. In contrast to Lgr4 null mice with 129Ola × C57BL/6J mixed background, C57BL/6J-backcrossed Lgr4 null mice (Lgr4−/−) showed the severe phenotype of embryonic lethality and also had dilated tubules in kidneys at E16.5. Based on quantitative RT-PCR and in situ hybridization, branching morphogenesis at E15.5 in the Lgr4−/− was arrested earlier, and both DBA-lectin staining and immunohistochemical analysis using Aqp3 antibodies showed that the ureteric bud (UB) of Lgr4−/− kidneys underwent premature differentiation. Furthermore, quantitative RT-PCR and histological analysis suggested that the impaired UB differentiation was caused by down-regulation of the Wnt pathway and Gata3 in the Lgr4−/− kidneys. We demonstrate here that Lgr4 has a novel function for maintaining the UB in an undifferentiated state. Developmental Dynamics 240:1626–1634, 2011. © 2011 Wiley-Liss, Inc.