Methanesulfonicacid hydrazide (a sulfonamide compound, msh: CH3SO2NHNH2) derivatives: methylsalicylaldehydemethanesulfonylhydrazone (5msalmsh), 5-methyl-2-hydroxyaceto-phenonemethane-sulfonylhydrazone (5mafmsh) and their Ni(II), Co(II) complexes have been synthesized for the first time. The structure of these sulfonamide compounds has been investigated by using elemental analyses; FT-IR, H-1 NMR, C-13 NMR, LC-MS, and UV-Vis spectrometric methods; magnetic susceptibility; conductivity measurements; thermal studies. The crystal structure of 5msalmsh has been investigated by X-ray analysis. The antibacterial activities of synthesized compounds were studied against gram positive bacteria: Staphylococcus aureus, Bacillus subtilis, and Bacillus magaterium; and gram negative bacteria: Salmonella enteritidis, and Escherichia coli by using the microdilution broth method. The biological activity screening showed that ligands have more activity than complexes against the tested bacteria. (C) 2008 Elsevier B.V. All rights reserved.