Plasmid mediated AmpC beta-lactamases are reported from Enterobacteriaceae with increasing frequency. There have been reports of treatment failures in patients infected with these organisms and given broad-spectrum cephalosporins. The aim of this study was to investigate the presence of plasmid mediated AmpC beta-lactamases in Escherichia coli and Klebsiella spp. A total of 41 strains of cefoxitin resistant or intermediate E. coli (n= 27) and Klebsiella spp. (n= 14) were collected from january 2005 to January 2006 at Akdeniz University Hospital Central Laboratory. Three-dimensional test was used as a phenotypic confirmatory test. Analytical isoelectric focusing electrophoresis was used to measure the pl values of the beta-lactamases. Plasmid mediated AmpC enzyme genes were amplified using multiplex polymerase chain reaction and sequenced by Beckman Coulter CEQ 8000. AmpC beta-lactamases were only detected in two isolates (7.4%) of E. coli. These isolates produced CMY-2 like enzymes and have either CTX-M or TEM enzyme. Transferable AmpC beta-lactamases are associated with multiple antibiotic resistance. Therefore detection of these enzymes in gram-negative bacteria has a clinical importance, since it can often provide valuable information to clinicians leading to more effective and appropriate use of antimicrobials.