In our study, efficiacy of disinfectans used commonly in our country has been investigated against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae strains which is most frequntly agent isolated from nosocomial infections in Kocaeli University Medical Faculty Hospital (KOÜ). Four different bacteria isolated from nosocomial infections and standart bacteria strains have been inoculated onto Mueller-Hinton agar at 10⁹, 10⁷,10⁵ cfu/ml concentrations. Equal volumes of disinfectants and serum physiologic as a control have been put into holes created on the surface of agar. According to suggestions of manufacturers, disinfectants have been applied sufficient time and cultures have been taken off from the edges of the holes. Their antibacterial effects have been evaluated both at times suggested by the manufacturers and after a day as inhibition zones. Only povidon iode (%7.5) has been found effective in all bacteria concentrations. In the evaluation of after a day, in all bacteria concentrations, formalin (%40) zone was ≥ 31mm and sodium hypochloride (%5) zone was ≥ 16 mm which were found more effective than the other disinfectants. The result that, disinfectants used in our study were less effective for nosocomial strains than for standard strains have been evaluated as a significant finding considering the hospital infections.