Abstract: Objective To study distribution,phenotypes and detection methodsof plasmid-mediated β-lactamases in Escherichia coli and Klebsiella pneumoniae.Methods Using routine antibiotics susceptibility tests for screening,extended spectrum β-lactamases (ESBL) confirm test for detecting ESBL,and cefoxitin three-dimension test for detecting plasmid-mediated AmpCs.Result Among 341 clinical isolates of Escherichia coli and Klebsiella pneumoniae,there are 164 strains (48.1%) showed MIC of cefpodoxime＞1 μg/ml by routine susceptibility test;102 strains of them were proceeded further detection,64 strains produced ESBL,only 6 strains were plasmidincode AmpCs.Conclusion The result indicated that ESBL (30.2%) were more than plasmid-incode AmpCs (2.8%) in plasmid-mediated β-lactamases in Escherichia coli and Klebsiella pneumoniae.