Abstract New metal complexes of the type [M(nih)(L)](PF6)n·xH2O and [M(nih)2](PF6)·xH2O (where M=Co(III) or Ni(II), L=1,10-phenanthroline (phen)/or 2,2′ bipyridine (bpy), nih=2-hydroxy-1-naphthaldehyde isonicotinoyl hydrazone, n=2 or 1 and x=3 or 2) have been synthesized and characterized by elemental analysis, magnetic, IR and 1H NMR spectral data. The electronic and magnetic moment 2.97–3.07B.M. data infers octahedral geometry for all the complexes. The IR data reveals that Schiff base (nih) form coordination bond with the metal ion through azomethine-nitrogen, phenolic-oxygen and carbonyl-oxygen in a tridentate fashion. In addition, DNA-binding properties of these six metal complexes were investigated using absorption spectroscopy, viscosity measurements and thermal denaturation methods. The results indicated that the nickel(II) complex strongly bind with calf-thymus DNA with intrinsic DNA binding constant Kb value of 4.9×104M−1 for (3), 4.2×104M−1 for (4), presumably via an intercalation mechanism compared to cobalt(III) complex with Kb value of 4.6×104M−1 (1) and 4.1×104M−1 (2). The DNA Photoclevage experiment shows that, the complexes act as effective DNA cleavage agent.