We evaluated the antioxidative activity of anthocyanins from an extract of the tuber of purple sweet potato (PSP) (Ipomoea batatas cultivar Ayamurasaki). Anthocyanins from PSP showed stronger 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity than anthocyanins from red cabbage, grape skin, elderberry, or purple corn, and eight major components of the anthocyanins from PSP showed higher levels of activity than ascorbic acid. In PSP anthocyanin-injected rats and PSP beverage-administered volunteers, DPPH radical-scavenging activity in the urine increased. The elevation of plasma transaminase activities induced by carbon tetrachloride was depressed in rats administered PSP anthocyanin solution. Two components, cyanidin 3-O-(2-O-(6-O-(E)-caffeoyl-beta-D-glucopyranocyl)-beta-D-glucopyranoide)-5-O-beta-D-glucopyranoside and peonidin 3-O-(2-O-(6-O-(E)-caffeoyl-beta-D-glucopyranocyl)-beta-D-glucopyranoide)-5-O-beta-D-glucopyranoside, which were detected in the plasma, protected low density lipoprotein from oxidation at a physiological concentration. These results indicate that PSP anthocyanins have antioxidative activity in vivo as well as in vitro.