Ni(II), Co(II) and Co(III) complexes of imidazole- and pyrrole-2-carbaldehyde thiosemicarbazone ligands (H2L1 and H2L2, respectively) have been prepared. The X-ray crystal structures of [Co(L1)(HL1)], [Ni(H2L1)2]Cl2 _ 3.5H2O and [Ni(HL2)2] have been solved. The Co(III) ion assumes a slightly distorted octahedral coordination geometry, involving both N2S binding domain of diand monoanionic ligand molecules. Whereas in [Ni(HL2)2] the metal ion is tetracoordinated in a square planar geometry by two pyrrole-2-carbaldehyde thiosemicarbazone molecules acting as NS-donor, the spatial array of non deprotonated H2L1 ligand molecules in [Ni(H2L1)2]Cl2 _ 3.5H2O is equivalent to that found for [Co(L1)(HL1)]. The in vitro antimicrobial properties of the ligands and their complexes were tested against representative bacterial and fungal strains in broth culture. The compounds H2L2 and [Co(L2)(HL2)(H2L2)] _ 1.5H2O exhibit a moderate inhibitory effect on the microbial proliferation and only against some Gram positive bacteria.