In the course of the investigations of natural antioxidants, we examined the antioxidant activities of the methanol (MeOH) extracts of some selected Prunus species, including P buergeriana, P davidiana, P padus, P pendula for. ascendens, P. sargentii, P. serrulata var. spontanea and P. yedoensis by three methods as represented by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, total ROS (reactive oxygen species) and the peroxynitrite (ONOO-) scavenging activity tests. We also evaluated the activities of the organic solvent-soluble fractions, including the dichloromethane (CH2Cl2), ethyl acetate (EtOAc), n-butanol (n-BuOH) fractions and the water (H2O) layer of P serrulata var. spontanea leaves. By means of bioassay-directed fractionation, we isolated eleven known flavonoids (1-11) from the EtOAc soluble fraction of the MeOH extract of the Prunus serrulata var. spontanea leaves, exhibiting strong antioxidant activity and characterized as prunetin (1), genistein (2), quercetin (3), prunetin 4'-O-beta-glucopyranoside (4), kaempferol 3-O-alpha-arabinofuranoside (5), prunetin 5-O-beta-glucopyranoside (6), kaempferol 3-O-beta-xylopyranoside (7), genistin (8), kaempferol 3-O-beta-glucopyranoside (9), quercetin 3-O-beta-glucopyranoside (10) and kaempferol 3-O-beta-xylopyranosyl-(1-->2)-beta-glucopyranoside (11). Compounds 3 and 10 showed good activities in all tested model systems. Compounds 2 and 8 showed scavenging activities in the DPPH and ONOO- tests, while compounds 5, 7, 9 and 11 were active in the ONOO- and ROS tests. On the other hand, compounds 1, 4 and 6 did not show any activities in the tested model systems.