The complexation processes between Cu-II and the antiviral drug, valacyclovir hydrochloride (H2L), were studied under different reaction conditions, using UV-Vis, IR and mass spectra, magnetochemical, thermogravimetric, atomic absorption, conductivity, and elemental analysis data. Using the Job method, the compositions of these complexes were determined. Under the ligand (H2L) excess (M:L = 1:1-1:10). In aqueous solutions, a binuclear violet complex Cu-2(HL)(2)L(H2O)(4) is formed, with an octahedral structure. Under comparable amounts of the reagents, in MeOH solutions, a green mononuclear complex Cu(H2L)Cl-2 is formed. Protonation constants of the H2L, and stability constants of its Cu2+ complexes, were determined by potentiometric titration in H2O media at 25 +/- 0.02 degrees C under a N-2 atmosphere and ionic strength of 0.1 M NaCl. It has been observed that H2L has three protonation constants. The divalent metal ion Cu2+ forms stable 2:1 and 2:2 complexes with H2L. The antimicrobial activity studies of the valacyclovir and it's complexes have been studied against some gram positive species: (Corynebacterium xerosis, Bacillus brevis, Bacillus megaterium, Bacillus cereus, Mycobacterium smegmatis, Staphylococcus aureus, Micrococcus luteus, Enterococcus faecalis) and gram negative (Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Yersinia enterocolitica, Kluyveromyces fragilis, Saccharomyces cerevisiae, Candida albicans) bacteriaz.