Objective：To investigate the effect of sodium butytate （different concentrations） on the growth and proliferation of rat liver oval cell line WB-F344, and to discuss the conditions and rules for sodium butyrate-inducd WB-F344 cells differentiation into biliary lineage in vitro. Methods： WB-F344 cells were treated with sodium butyrate （0.75, 2.25, 3.75, 4.5 mmol/L） and the cell growth and morphological changes were observed; routinely cultured WB-F344 cells were taken as control. The changes of CK19 protein expression were examined immunohistochemically after WB-F244 cells were treated with 3.75% sodium butyrate; and the expression of phenotypic markers, such as 7-glutamyltransferase （GGT） ,β4-integrin, CK19, AFP and ALB at mRNA level were determined by RT-PCR. Untreated WB-F344 cells were used as blank control. Results： We found that sodium butyrate inhibited the growth of WB-F344 cells. The optical densities were significantly decreased in 3.75 and 4. 5 mmol/L groups compared with that in control group（P〈0.01）; but no significant difference was found between 0. 75, 2.25 mmol/L groups with control group. WB-F344 cells treated with 3. 75, 4. 5 mmol/L sodium butyrate became larger and round, with increased nuclei and decreased nucleus to cytoplasm ratio; those treated with 0.75, 2.25 mmol/L had no obvious changes. Immunohistochemical results showed that sodium butyrate significantly increased CK19 expression compared with control group（92.3±1.1]% vs [1. 3±0. 2]% , P〈0.01）. RT-PCR showed increased expression of β4-integrin in sodium butyrate treated groups, but not in control group; the expression of GGT and CK19 was higher than that of control group. Alpha-fetoprotein （AFP） expression was observed in blank control group, but not in sodium butyrate treated cells. Albumin expression was not detected in the 2 groups. Conclusion.. Sodium butyrate at 3. 75 mmol/L is suitable for inducing WB-F344 cells differentiate into the biliary lineage in vitro