The aqueous ethanolic extract of Eucalyptus leaves were used as the antioxidant in food additives, but it was not all clear of antioxidative components. In this paper, two tautomerizing gallotannins with strong antioxidant activity were isolated from the eucalyptus leaves extract. The antioxidant activities of the two components were more than two times that of the standant antioxidant Trolox (ORAC index). The chemical structures were determined by HPLC, H-NMR and 13C-NMR. The results have shown that one is 3-galloyl-4,6-HHDP-D-glucose (Gemin D), and the other is 2，3，4，6-two-HHDP-D-glucose（Pedunculagin）, and the former component is the first to be isolated from this plant.