The present study was conducted to evaluate the antibacterial activity of aqueous extract and essential oil obtained from Eucalyptus globulus leaves. The aqueous extract was obtained by decoction in volume of distilled and essential oil by hydrodistillation method. The antibacterial effect was studied in vitro in five strains: Klebseilla pneumoniae ATCC10031 and four multi-resistant strains of Klebseilla pneumoniae isolated from hospitalized patients. Minimum inhibitory concentration (CMI) and minimum bactericidal concentration (MBC) was determined by agar dilution method. The essential oil has demonstrated a good antibacterial activity against all strains tested with best inhibition zone equal to 18,5±2,12mm for 5ɥl and 32,50±0,70mm for 10ɥl. Studied aqueous extract showed a considerable antibacterial effect less than essential oil of the some plant, when the best inhibition zone was 10,0±1,41mm for 5ɥl and 13,5±0,70mm for10ɥl. The MIC and MBC of essential oil was ranging respectively from 100 to 400ɥg/ml and 200ɥg/ml to 500ɥg/ml, and for aqueous extract from 300 to 400ɥg/ml and 400 to 500ɥg/ml. The results obtained indicated that Eucalyptus globulus essential oil could be used as a potential source of naturel antibiotic for raising problems of infectious diseases caused by multi-resistant Klebseilla pneumoniae after testing the toxic effects on human.