ObjectiveTo investigate the common bacteria and change in antimicrobial resistance in an intensive care unit (ICU) in the past 5 years, and provide evidence for rational use of antimicrobial agents.MethodsBacteria isolated from ICU patients in a tertiary firstclass hospital from 2009 to 2013 were collected, identified, and performed antimicrobial susceptibility testing.ResultsA total of 1 196 bacteria isolates were isolated in 2009-2013, the top five species were Acinetobacter baumannii (A. baumannii, 29.60%), Pseudomonas aeruginosa (P. aeruginosa, 14.38%), Staphylococcus aureus (S. aureus, 12.21%), Escherichia coli(E. coli, 12.21%), and Klebsiella pneumoniae(K. pneumoniae, 11.37%). Resistance rates of S. aureus to oxacillin, gentamycin, clindamycim, ciprofloxacin, and rifampicin showed a decreasing tendency from 2009 to 2013(all P＜0.05)， and no strain was detected to be resistant to vancomycin during 5 years. Resistance rates of P. aeruginosa to ceftazidime, cefepime, aztreonam, gentamycin, amikacin, tobramycin, and piperacillin/tazobactam decreased gradually (all P＜0.05), imipenem resistance rates were 32.26%-46.43% in 2009-2012 and 16.00% in 2013; A. baumannii  maintained a low level resistance to amikacin, tobramycin, and compound sulfamethoxazole（all P＜0.05），resistance rates to imipenem were all >80% in 2009-2011 and 10.53% in 2013, A. baumannii had high resistance rates to most antimicrobial agents(resistance rates were >80%) during 5 years. Resistance rates of K. pneumoniae  and E. coli to piperacillin/tazobactam, cefazolin, cefepime, amikacin, and  aztreonam had a decreased tendency in 2009-2013(all P＜0.05).ConclusionThe common bacteria causing infection in the ICU of this hospital showed a downward trend， which may be related to the introduction of national policies and management of hospital, continuous management of antimicrobial agents is suggested, antimicrobial agents should be used rationally to prevent the increase of bacterial resistance.