Inactivation of the C/EBPα gene (Cebpa) in the mouse not only causes impaired hepatocyte maturation, but also induces pseudoglandular structures in the liver parenchyma. The present study was undertaken to determine how the expression of other transcription factors controlling differentiation into hepatocytes and biliary epithelial cells is affected, and how the hepatic architecture, including the bile and vascular systems, is disordered in the fetal knockout liver. Histochemical analyses demonstrated that the expression of HNF1α and HNF4α was heterogeneous in the knockout liver, and that not all parenchymal cells (pseudoglandular) expressed these transcription factors, whereas parenchymal cells in the wild-type liver homogeneously expressed these transcription factors. SOX9, which was expressed only in biliary cells in the wild-type liver, was detectable in many pseudoglandular cells of the knockout liver. Although the pseudoglandular cells often coexpressed SOX9 and HNF1α/HNF4α, cells expressing SOX9 but not expressing HNF1α/HNF4α (biliary cells) were sometimes detectable in the parenchyma. Periportal biliary structures were abnormal in their segregation from the parenchyma and in their expression of the transcription factors and Ep-CAM, a biliary adhesion molecule. These results suggest that the inactivation of the Cebpa gene causes unstable expression of liver-enriched transcription factors or biliary transcription factors and elevated expression of Ep-CAM, which may lead to abnormal biliary morphogenesis in the knockout liver. The impaired maturation of the parenchyma caused elevated expression of PECAM-1, desmin and Foxf1, suggesting that the maturation of the parenchyma plays an important role in the normal histogenesis of nonparenchymal cells (stellate cells and sinusoidal endothelial cells).