Abstract: The isoflavone was purificated from byproducts of enzyme- assisted alcohol leaching soybean oil by organic solvent extraction and resin adsorption. The purity of isoflavone was investigated by high performance liquid chromatography( HPLC). The human breast cancer cell line MCF- 7 was used as the model cells and the affect of soybean isoflavone on the proliferation of MCF-7 cells were studied.The result showed that the optimum extraction solvent for purification of soybean isoflavone was ethyl acetate and n- butyl alcohol mixture( 1∶ 1) and the extraction rate and purity of isoflavone were 70.47% and 26.45%,respectively. The optimum conditions of resin adsorption for extraction of isoflavone were as follows: the adsorption resin was LSA-8,the concentration and flow rate of the sample were 0.8 mg / m L and 0.5 BV / h,respectively,the eluent solution was 75% ethanol and the flow rate and volume of eluent solution were 6 BV / h and 1.5 times of the sample volume,respectively.The extraction rate and purity of soybean isoflavone under the optimal condition of resin adsorption extraction were 83.71% and72.09%,respectively.The MCF- 7 cell experiments suggested that when the concentration of soybean isoflavone was up to 100 mg / L,it could significantly inhibit the proliferation of human breast cancer cell. And the anticancer function of soybean isoflavone was concentration- dependent.