A new tetradentate ligand incorporating dioximes has been synthesized. The dioxime, (H2L) was characterized by elemental analysis, H-1-NMR, C-13-NMR, IR, and mass spectral data. In addition, its copper(II), nickel(II), and cobalt(II) complexes have been prepared and characterized by physical and spectral methods. Elemental analyses and spectroscopic data of the metal complexes are consistent with the proposed structures. The crystal structure of the Co(II) complex (7) was determined by single-crystal X-ray diffraction technique. The inhibitory activities of compounds were examined. Biological activities of the ligand and its metal complexes were tested and the ligand and its metal complexes had inhibitory activity against G(-) Staphylococcus aureus and Pseudomonas aeruginosa.