An armA-producing Klebsiella oxytoca isolate, strain 157, was detected after screening of 447 extended-spectrum beta-lactamase-producing Enterobacteriaceae isolates in China. K. oxytoca 157 was resistant to aminoglycosides, ciprofloxacin and most beta-lactams. Resistance to aminoglycosides and beta-lactams could be transferred to recipient Escherichia coli by conjugation. armA, blaCTX-M-15 and blaTEM-1 genes were detected in K. oxytoca 157 and transconjugant E. coli strain 600(pEC157). Mutation of aa 87 in GyrA was found in K. oxytoca 157. A plasmid of approximately 55 kb was extracted from K. oxytoca 157(pKO157) and E. coli 600(pEC157). Southern blot hybridization confirmed that the armA, blaCTX-M-15 and blaTEM-1 genes were all located on this conjugative plasmid (pEC157). PCR mapping was also performed to investigate the genetic environment of armA. The armA gene was found to be flanked by the same putative transposable elements as reported previously in E. coli, Klebsiella pneumoniae and Citrobacter freundii isolates from different countries.