The extraction and concentration of isoflavones from defatted soy flour (DSF) is attempted by leaching, membrane process and liquid-liquid extraction. The optimized extraction conditions by response surface methodology (RSM) resulted in an isoflavone content of 3.2mg/g of DSF. The extracted isoflavones are processed by ultrafiltration for preliminary purification resulting in 3.0mg/g of DSF, and then concentrated by liquid-liquid extraction with diethyl ether (4.8mg/g DSF). The final isoflavone content is 69mg/g of dried extract with an overall recovery of 57.5%. The optimization of extraction conditions resulted in an about 2.5 fold enhancement of isoflavones and concentration step enriched the isoflavones by about 8.5 fold compared to initial extract.