PURPOSE: Cytotoxicity of the bile acids on colon cancer cell lines was studied to know which bile acid was most cytotoxic to colonic mucosal epithelium. We performed agarose gel electrophoresis whether this toxicity was caused by detergent effect of the bile acids or by apoptotic pathway. MATERIALS AND METHODS: HT29, LoVo, SW620 colon cancer cell lines were exposed to lithocholate, cholate, deoxycholate and chenodeoxycholate with 50, 100, 150, 200, 250, 300 pM as final concentration in DMEM culture media for short time (for 2 hours) and for long time (for 5 days). Agarose gel electrophoresis was performed on each colon cancer cell lines (HT29, LoVo, SW620, SW480) after 1, 2, 3, 4, 5 days exposure to deoxycholate with 150 pM concentration to detect intemucleosomal fragmentation. RESULTS: There was no toxicity after short time exposure in all bile acids concentration and in all colon cancer cell lines. Of the bile acids, deoxycholate was most toxic for all colon cancer cell lines. And DNA fragmentation was noticed after 2 days exposure with deoxycholate. Only LoVo cell line showed apoptotic DNA pattern after 4 days of exposure with deoxycholate. CONCLUSION: Bile acids (especially deoxycholate) are suggested to be possible agents to cause apoptosis in colonic mucosal epithelium.