Schiff bases have been synthesised by the reaction of salicylaldhyde, 5-bromosalicylaldehyde, 5-nitrosalicylaldehyde and naphthaldehyde with thiosemicarbazide. The ligands of N,N'-bis(salicylidene)thiosemicarbazide (1) react with Mn-II, Co-II, Ni-II, Cu-II, Zn-II and Hg-II metals to yield 1 : 1 metal-ligand complexes. The structures of ligands and complexes have been investigated by elemental analyses, magnetic susceptibility measurements, H-1 NMR, IR and UV-visible spectral data. The pentadentate nature of the ligands is inferred from IR spectra. The UV-visible spectral data suggest octahedral geometry for Mu(II), Co-II, Ni-II, Cu-II, square-pyramidal geometry for Zn-II and Hg-II The antimicrobial activities of the ligands and metals complexes have been screened in vitro against the organisms Escherichia coli ATCC 11230, Staphylococcus aureus ATCC 6538 P, Bacillus cereus ATCC 7064, Proteus vulgaris ATCC 8427, Salmonella typhimurium DSM 554, Corynebacterium xerosis ATCC 373 and Hanseniaspora guilliermondii DSM 3432, Rhodotorula rubra DSM 70403 and Kluyveromyces fragilis ATCC 8608. It is observed that the coordination of metal ions has pronounced effect on the microbial activities of the ligands. The metal complexes have higher antimicrobial effect than the free ligand.