The content of genistein and daidzein which were known to be major antioxidative compounds in soybeans were detected by $C_{18}$ reverse phase HPLC. Most of isoflavones in soybeans were detected in the methanol extract but much less amount of isoflavones in the water extract. Among the four different kind of soybeans, the isoflavone content was highest in brown soybean, followed by yellow, small black and black soybean, in the order. These isoflavones were known to be soluble in hot water, which means transfer of isoflavone content was highest in brown soybean, followed by yellow, small black and black soybean, in the order. These isoflavones were known to be soluble in hot water, which means transfer of isoflavones in soy curd into whey during soy curd processing. To identify the change of isoflavone content during processing of soybean curd, soybean curd were made from yellow, brown and black soybean and isoflavone content were determined in each soybean curd, curd residue and whey. Most of soflavones were remained in the whey, it means most of useful antioxidative compounds were wasted. Thus, it is necessary to develop new technology to collect these isoflavones lost during soybean curd processing.