Objective To 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.Methods Bacteria isolated from ICU patients in a tertiary first-class hospital from 2009 to 2013 were collected,identified,and per-formed antimicrobial susceptibility testing.Results A 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).Conclusion The common bacteria causing infection in the ICU of this hospital showed a down-ward 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 in-crease of bacterial resistance.