A methanol extract of mulberry cake prepared from mulberry fruits (Morus spp.) was shown to have strong scavenging activities against DPPH, superoxide and hydroxyl radicals. Eleven phenolic compounds were isolated from the mulberry cake by a combination of Diaion HP-20, silica gel (or polyamide), Sephadex LH-20 column chromatographies, preparative HPLC and TLC. Their chemical structures were characterized as procatechuic acid (PCA), caffeic acid (CA), cyanidin 3-O-$eta$-D-glucopyranoside (CyG) and cyanidin $3-O-eta­D-rutinoside$ (CyR), rutin (RT), isoquercitrin (IQT), astragalin (AG), quercetin (QT), morin (MR), di-hydroquercetin (DHQ), and 4-prenylmoracin (PM) by spectral analysis and the published data. Most of the phenolic constituents were effective scavengers of DPPH, superoxide and hydroxyl radicals, and especially caffeic acid and 4-prenylmoracin showed potent superoxide and hydroxyl radical scavenging activity, in which their activities were higher than that of the well-known antioxidant, BHT (p< 0.05). Dehydroquercetin and quercetin also exhibited strong superoxide and hydroxyl radical scavenging activities. These results suggest that mulberry cake containing antioxidant phenolic compounds may be useful as natural antioxidants in functional foods and cosmetics.