Thiosemicarbazone ligands and related metal complexes have experienced long standing applications in biology and medicine, presenting a great variety of biological activity including antibacterial, antifungal, anti-inflammatory and anticarcinogenic properties [1-3]. In this work we present two ligands (2-hydroxy-3carboxynaphthalidenethiosemicarbazone (H3L1) (1) and (2-hydroxy-3carboxynaphthalidene-4-phenylthiosemicarbazone, (H3L2 ) (2) and their copper(II) complexes with composition [Cu(H2L1)Cl]-Solv (3), [Cu(H2L1)Cl]-dmf (4), [Cu(H2L1)NO3(dmf)] (5), [Cu(HL2)(Et)] (6), [Cu(HL2)(dmso)] (7) (figure) that were screening for their in vitro antimicrobial activity (MIC, MBC) against some representative medically important bacterial strains namely S. aureus, C. albicans, E. coli , K. pneumonae. The compounds 1, 4, 5, 7 were characterized by single crystal X-ray analysis [4, 5]. The antimicrobial activity was evaluated using successive dilution method for MIC and agar-cup method for MBC determinations in dimethylsulfoxide solvent. The activity data show that thiosemicarbazone copper(II) complexes are more potential antimicrobials than their parent Schiff base ligands. The free 1, 2 ligands have an inhibitory effect in the ranges (MIC 60-120 μg/ml; MBC 120-250 μg/ml) and (MIC 250-500 μg/ml; MBC 500 μg/ml) against Gram-positive G(+) and Gram-negative G(-) strains respectively. The results revealed moderate activity (MIC 259-500 μg/ml) against G(-) bacteria (E. coli, K. pneumonae) for all complexes with the exception of complex 7 with MIC 60 μg/ml and MBC 120 μg/ml for E.coli strain. The highest antibacterial activity of the complexes was observed against G(+) bacteria (S.aureus, MIC 15- 120 μg/ml; 3, 4, 6), (C.albicans, MIC 15-30 μg/ml; 3, 4). Different effects of the compounds were found for the bacterial strains suggesting that the antimicrobial activity depends on the presence of copper ion, the composition of the acid residue and the bulkiness of group attached to the thiosemicarbazone moiety. It was determined that the minimal bactericidal concentration changes in the following way H3L2 > H3L1 ; Cl- > NO3 - . Antibacterial efficiency of the tested compounds decreases from G(+) to G(-) bacteria.