ObjectiveTo investigate the AmpC enzyme production in Enterobacter cloacae (E. cloacae) of a hospital, and drug resistance of E.cloacae to 10 kinds of commonly used antimicrobials, so as to guide clinical rational choice of antimicrobials. MethodsNinetyeight strains of nonrepeat clinical isolated E.cloacae were collected from the hospital from August 2007 to July 2008,  cefoxitin disk diffusion method was used to screen AmpC enzyme, AmpC enzyme of E.cloacae was confirmed by enzyme extract threedimensional highyield tests, the AmpC enzyme gene was detected with polymerase chain reaction. Resistance of drugs was detected by KirbyBauer agar diffusion method．ResultsAmong 98 clinical isolated E.cloacae，36 strains produced AmpC βlactamases,the detection rate was 36.73%. In 36 AmpCpositive strains, 6 only carried DHA gene (16.67%); 20 only carried ACC gene (55.56%);  8 carried ACC and MIR gene together (22.22%); 2 carried ACC, MIR and FOX genes together (5.56%). AmpCpositive strains were almost resistant to cefoxitin, and were sensitive to third generation cephalosporins, enzyme inhibitors, aztreonam, amikacin and ciprofloxacin with varying degrees(44.44%~91.67%), but sensitive to cefepime and imipenem, drug resistant rate was 27.78% and 0.00% respectively. ConclusionE.cloacae carries high rate of AmpC enzyme, which is the main cause of drugresistance to the third generation  cephalosporins, treatment of  E.cloacae infection should be based on the results of antimicrobial susceptibility test.