Abstract: Class 1-3 integrons from 87 strains of Escherichia coli, Salmonella, Riemerella anatipestifer and staphylococci isolated from pigs and ducks were screened and the variable regions of the class 1 and 2 integrons were amplified. No class 3 integrase gene fragments were amplified from any of the 87 strains; class 2 integrase gene fragments were amplified from only seven strains and no class 2 integron variable region gene cassettes were amplified. Class 1 integrase gene fragments were detected in 65 strains and variable region gene cassettes were amplified from 26 strains which were confirmed by sequencing to be the aadA2, dfrA12-orfF-aadA2, dfrA17-aadA5, aacA4-catB8-aadA1 and dfrA32-ereA-aadA2 gene cassettes. The 87 strains were tested for drug susceptibility to 10 kinds of antibiotics using the Broth Microdilution Method and minimum inhibitory concentrations. There was no significant difference in the resistance phenotypes of strains carrying gene cassettes and those not carrying gene cassettes and there was no correlation between the antibiotic resistance of a strain and whether it carried a resistance-gene cassette. The integron-mediated horizontal transfer of resistance genes might be just one resistance mechanism acquired by bacteria during their evolution and may not play a major role under the selection pressure exerted by the wide variety and high concentrations of antibiotics used at present, whereas it may play a synergistic role.