Background/Aims: The cell homeostasis is regulated by a balance between apoptosis, proliferation and growth arrest. Bcl-2 and Bax belong to a family of cytoplasmic proteins that regulate apoptosis. The aim of this study was to verify blood biochemistry, histologic findings and expression pattern of Bcl-2 and Bax during the bile duct proliferation. Methods: We induced bile duct proliferation by the bile duct ligation in Sprague-Dawley rats. The expression of Bcl-2 and Bax was visualized by immunohistochemical staining. The rats were sacrified 2, 4, 6, 8 weeks after bile duct ligation. Results: Bcl-2 was expressed in the bile duct of control rats (n=10) and bile duct- ligated rats (n=40). Bcl-2 expression in hepatocytes was noted in the bile duct-ligated rats but not in control rats. Bax was expressed in the bile duct and hepatocytes of the control and bile duct-ligated rats. Histologically, bile duct proliferation became infiltrative and accompanied periductal inflammatory cells in the bile duct-ligated rats. However, serum levels of AST, ALT, and bilirubin were not increased according to duration of bile duct ligation. Conclusions: From these results, we suggest that hepatocellular expression of Bcl-2 after ligation is an adaptive phenomenon to resist apoptosis and expression of Bax in bile duct is due to inflammatory process. (Korean J Gastroenterol 2001;37:277-282)