Objective To observe effects of Genistein and 5fluorouracil(5-FU) on human colon carcinoma cell line Colo320.Methods The MTT assay and median-effect principle were used.Results The two drugs were antagonistic at higher concentrations and synergistic at lower concentrations,The sequence and time of drug administration can influence the effects of the two drugs on Colo320.Conclusion The two drugs were cooperated at lower concentrations and antagonistic at higher concentrations.The sequence and time of drug administration were also important for their effects on the cells.