Six complexes, M(HL)2 · nH2O (M=Co, Ni and Fe; n=4) with two ligands, 2-carboxy-benzaldehydebenzoylhydrazone (H2L1) and 2-carboxybenzaldehyde-(4′-methoxy)benzoylhydrazone (H2L2), have been synthesized and characterized on the basis of elemental analyses, molar conductivities, i.r. spectra and thermal analyses. In addition, the suppression ratio for O2- (a) and the suppression ratio for OH· (b) were determined with a 72 spectrophotometer. The 50% inhibition [IC50 (a) and IC50 (b)] of the complexes were studied. This study demonstrated that the complexes have activity in the suppression of O2- (a) and OH· (b). In general, the antioxidative activities increased as the concentration of these complexes increased up to a selected extent. The complexes exhibit more effective antioxidants than the ligands and the series of the ligand (H2L2) are better than the series of the ligand (H2L1) do.