Thiosemicarbazones and their metal complexes are a wide class of biologically active compounds. In the present work, we report the synthesis, structure, and antibacterial property of copper(II) with 8-formilquinoline 4-etylthiosemicarbazone (4-Et-HQATSC). Copper(II) nitrate and 4-Et-HQATSC were dissolved separately in ethanol, and mixed together in equimolar ratio. The final product has the composition Cu(4-Et-HQATSC)(NO3)2. The structure of Cu(4-Et-HQATSC)(NO3)2 is molecular. It consists of discrete molecules in which the coordination sphere is formed by the neutral ligand 4-Et-HQATSC, and two monodentate ions NO3 - , coordinated througth an oxygen atom.schemeIntroduction of ethyl substituent at the nitrogen marginally atom in the thiosemicarbazidic fragment haven’t change the coordination mode of the organic ligand [1]. The base of the tetragonal pyramid is formed by three atoms of the tridentate 4-Et-HQATSC ligand coordinated via NNS donor sites and by one oxygen atom of the nitrate anion. The second NO3 - ion is situated in the apical position. The bond distance Cu-O = 1,994 Å for the ligand coordinated in the equatorial plane is smaller, than interatomic distance Cu-O = 2.431 Å in the apical position. The antimicrobial activity against gram-negative and gram-positive bacteria has been determined for this compound. The results clearly demonstrate than the antibacterial activity of Cu(4-Et-HQATSC)(NO3)2 against Pseudomonas aeruginosa are more than 2 times higher, against Escherichia coli and Enterococcus faecalis 4 times higher, against Proteus vulgaris 64 times higher and against Staphylococcus aureus 12 times higher when compared to the activity of furaciline. The presence of ethyl-substituent in the thiosemicarbazide moiety gives rise to an increasing of the antibacterial activity.