To investigate the mechanism of ursodeoxycholic acid (UDCA) in hepatocyte apoptosis using differentiated hepatocytes derived from bone marrow mesenchymal cells.Rat bone marrow mesenchymal cell was induced into mature hepatocytes in vitro and then treated with PBS (Cont), deoxycholic acid (DCA), DCA plus UDCA (U + D) or UDCA alone (UDCA). Cell apoptosis was detected by Hoechst staining and Caspase-3 activity measurement. The mRNA expressions of p53 and Bax were measured by semi-quantitative RT-PCR and real-time RT-PCR. The Bax protein expression was detected by immunohistochemistry.In comparison with Cont, DCA obviously induced hepatocyte apoptosis as measured by an increased cell count and a higher Caspase-3 activity (P < 0.05). These increments could be inhibited by addition of UDCA. The expressions of p53 and Bax in hepatocytes were up-regulated by DCA. These up-expressions could also be inhibited by UDCA. The DCA-induced increased count of Bax-positive cells could be reduced by UDCA.UDCA inhibits DCA-induced hepatocyte apoptosis by down-regulating the expression of p53/Bax signal molecule.