Two new octahedral [Ni(phen)2(dppz‐idzo)]2+ and [Co(phen)2(dppz‐idzo)]3+ complexes have been synthesized and characterized by CHN analysis, electrospray ionization‐MS, nuclear magnetic resonance, and UV–Vis spectra. The DNA‐binding ability of these complexes was spectrophotometrically, hydrodynamically, and electrophoretically evaluated which indicated that they strongly intercalate into the DNA double helix, and that both induced severe DNA damage in the presence of peroxide. The complexes also showed strong antiproliferative effect against HepG2 and MDA‐MB‐231 cells. By contrast, they were found to be inactive against the MCF‐7 cell line. The ligand itself was found to be inactive against the cells tested.