The antioxidant activity, nitrite scavenging effect, and angiotensine I-converting enzyme inhibiting activity of solvent extracts of soybean isoflavone were investigated. Also anticarcinogenic activities of them were examined by MTT assay using human cancer cell line. Isoflavone aglycones showed relatively high antioxidant activity in order of glycitein, genistein, and daidzein. Methanol extract of soybean actively scavenged free radicals and was shown excellent nitrite scavenging effect. Glycitein and methanol extract of soybean inhibited the growth of human cancer cell such as stomach carcinoma (SNU-1) and colon carcinoma (SNU-C4) effectively. Genistein, daidzein and methanol extracts of soybean inhibited the growth of cancer cell such as stomach carcinoma (SNU-1), but had weak activities to colon carcinoma (SNU-C4). To applicate the soybean isoflavone as an enhancer for food quality and processibility, the stabilities on heat and pH of isolated isoflavone, isoflavone in soybean flour and isoflavone concentrate of soybean were investigated. Stability of isoflavone concentrate of soybean was decreased in pH extreme (below 3, above 8) during sterilization, but isoflavone in soybean flour showed higher stability in all pH range. All kinds of isoflavone tested in this study were very stable during the heat treatment.