Este artigo descreve a síntese e a caracterização de três novos complexos de platina(II) com a oxitetraciclina, doxiciclina e clortetraciclina por análise elementar, espectroscopias IV e RMN de II ions as a function of the pH were studied by 1 H NMR. All the investigated tetracyclines form 1:1 complexes with Pt II via the oxygen of the hydroxyl group and oxygen of the amide group at ring A. The minimal inhibitory concentrations (MIC) of the ligands and those of their Pt II compounds were determined in two sensitive strains (E. coli HB 101 and E. coli ATCC 25922) and in a resistant one (E. coli HB101/ pBR322). Platinum complex of doxycycline is twice as potent as the free antibiotic in the resistant strain. Octanol/water partition coefficients of the complexes were determined. Increasing lipophilicity enhances antimicrobial activity in the resistant strain.