Ninety-four percent of 336 strains of Klebsiella pneumoniae were resistant to ampicillin, while less than 10% were resistant to cefotaxine and ceftazidine. Among all the aminoglycosides tested, amikacin had the strongest activity on K. pneumoniae. The resistant rate of nosocomial strains was higher than that of community strains. The results of susceptibility test showed that 42% (119/280) of K. pneumoniae strains were gentamicin-resistant. Based on the resistant pattern of K. pneumoniae, the aminoglycoside-modifying enzymes produced by the organisms were inferred. Among them 90% of 119 strains produced aminoglycosides-modifying enzymes AAC (3)-V, 8% (10/119) AAC (3)-V together with AAC (6')-Ib, AAC (6')-V or ANT (2"). The resistance of two strains was assumed to be permeability change. Besides, 58% (161/280) were sensitive strains without producing any aminoglycoside-modifying enzymes. Bacteria typing done by phage typing or Klebcin in 27 strains showed that most strains were from different origins with few exceptions. The results show the significance for controlling the nosocomial infections and reasonable use of antibiotics.