< Introduction > This study was designed to test the hypothesis that autoimmunity to PDC-E2 or BCKD-E2 itself can induce the pathology of PBC.< Methods > Neonatally thymectomy (NTx) was performed 2 days after birth. The mice in group A were immunized with a mixture of recombinant PDC-E2/BCKD-E2 hybrid molecule (150μg) and FCA after NTx. The mice in group B were immunized with hybrid molecule and FCA without NTx. The mice in group C were immunized with a mixture of hybrid molecule and FCA after NTx and LPS (0.5μg) was injected intravenously 2 days after each immunization.< Results > The mice in group C showed positive AMA and a high incidence of nonsuppurative cholangitis which is characterized by the mononuclear cell infiltration around the biliary epithelial cells.< Conclusion > PBC-like lesion is induced by immunization with PDC-E2 or BCKD-E2 proteins, and endotoxin such as lipopolysaccharide may augment the pathogenesis of PBC.