PURPOSE: Bile acids were considered as a promoting factor for colon cancers. It has been suggested that bile acids could promote cellular proliferation or apoptosis according to their concentration. Therefore, we studied the expression of cell cycle and apoptosis related proteins on HCT116 colon cancer cells according to different deoxycholic acid concentrations. METHODS: HCT116 colon cancer cells were incubated with low (20 micro M) and high (250 micro M) concentrations of deoxycholic acid for 72 hours. Cellular proliferation and toxicity were then measured by MTS assay. The expression of cell cycle and apoptosis related proteins was evaluated by Western blot analysis. RESULTS: In a low concentration of deoxycholic acid, the change of expression of the cell cycle related proteins-cyclin D1, cyclin E, cyclin A and CDK2 were similar compared with cultures that were without deoxycholic acid. In a high concentration of deoxycholic acid, cyclin A and cyclin D1 proteins were not expressed and the expression of cyclin E and CDK2 were decreased. The expression of survivin protein was increased by a low concentration of deoxycholic acid but it showed no significant difference when compared with cultures without deoxycholic acid. However in a high concentration of deoxycholic acid, survivin was not expressed. Deoxycholic acid has no effect on the expression of Bcl-2 and Bax proteins. CONCLUSION: A high concentration of deoxycholic acid can inhibit HCT116 colon cancer cell proliferation by suppressing the expression of all the cell cycle related proteins and also survivin, an inhibitor of apoptosis.