Fractionation of the methanolic and total oligomer flavonoid enriched extracts from Rhamnus alaternus leaves resulted in the isolation of three flavonoids: kaempferol 3-O-isorhamninoside (1), rhamnocitrin- 3-O-isorhamninoside (2) and rhamnetin-3-O-isorhamninoside (3), along with apigenin, kaempferol and quercetin. The structures were determined using data obtained from FAB–MS, 1H and 13C NMR spectra, as well as by various correlation experiments (COSY, HMQC and HMBC). The antioxidant activities of the isolated compounds were evaluated by measuring their ability to scavenge the DPPH radical and super- oxide anions, to inhibit H2O2-induced lipid peroxidation in human K562 cells, and to inhibit xanthine oxi- dase activity. Compound 3 was a strong scavenger of DPPH