Antibacterial activity of gentamycin sulfate was studied in vitro and in treatment of albino mice with experimental infections. Gentamycin was superior to kanamycin with respect to its antibacterial effect against clinical strains of Staphylococcus, Coli bacteria, Proteus and Ps. aeruginosa. High efficiency of gentamycin was found with respect to acute and chronic staphylococcal infection, acute Proteus and Coli sepsis. The antibiotic was characterized by low LD50, high chemotherapeutic index, rapid decrease in isolation of the causative agent from the animal organs. The activity of gentamycin against infections caused by Ps. aeruginosa was the main advantage of gentamycin in comparison to kanamycin.