We investigated the bioactive components and their biological activities of soymilk residue (SI) collected from the industry. Two drying methods, namely combined far-infrared radiation and hot-air drying (FIR-HA) and hot air drying (HA), were employed for reducing the moisture content of the residue. After drying, the contents of total phenolic, flavonoid isoflavone, daidzein and genistein of dried SI increased significantly when compared to untreated whole soybean and soy residue. The extracts were the most efficient in inhibiting α-amylase (85–96%), being involved in lowering starch digestion. The correlations between different phenolic fractions of soy residue extract and biological activities as well as starch digestibility were reported. We suggest that SI could be used as an ingredient in functional foods, thus providing added health-promoting properties.