Objective. Analyze the etiological structure of infectious complications in patients with acute leukemia and determine the sensitivity to antibacterial drugs of the main pathogens.Materials and methods. The results of bacteriological cultures and antibiograms of 177 patients with acute leukemia and infectious complications for the period 2019–2021 were retrospectively studied.Results. In 2019, the frequency of isolation of Gr+ flora was 45.28% and Gr- was 54.72%; in 2020 the percentage of Gr+ bacteria was 34.62%, Gr− was characterized by 65.38%; in 2021 it was 41.3% and 58.7% respectively, (x2=0.20, p=0.66). In 2019, one of the main pathogens was Klebsiella pneumoniae (21%), which retained its positions by 2021 (13%; x2=0.05, p=0.82). The causative agent showed polyresistance to many antibiotics, except for imipenem (100%) and fosfоmycin (100%). In the period 2020–2021 Klebsiella pneumoniae began to compete with Stenotrophomonas maltophilia, which showed an increase in the detection rate from 11% to 17% (x2=29.46, p=0.0001). Having polyresistance, the pathogen showed 100% sensitivity only to ticarcillin/clavulanate and co-trimoxazole.Conclusion. In the absence of changes between the frequency of isolation of Gram-positive and Gram-negative microorganisms, the increase in the number of strains of Gram− microorganisms (K. pneumoniae and S. maltophilia) with multiple antibiotic resistance among the causative agents of infectious complications in patients with acute leukemia necessitates continuous microbiological monitoring to improve the tactics of antibacterial drugs.