Abstract: Objective:To study the AmpC beta-lactamase mediated by plasmid in enterobacter cloacae and its genic type.Methods:AmpC beta-lactamase in enterobacter cloacae was detected on the basis that AmpC beta-lactamase could be inhibited by 3-aminophenylboronic acid（APB）.Conjugation test was used to check the transfer of ampC gene mediated by plasmid.Multi-PCR and DNA sequence test was used to detect ampC gene and its genic type.The amplified ampC gene was sequenced and analyzed by EMBOSS software.Results:Among 59 clinical isolates of enterobacter cloacae insusceptible to cefoxitin and cefotaxime,there were 53 strains with positive AmpC beta-lactamase.Among them,3 transconjugants were obtained by conjugation test.PCR and DNA sequencing were further used to detect the ampC gene type of the three strains and their conjuants,which was analyzed to be DHA-1 type.Conclusion: 3 transconjugants are obtained successfully from AmpC beta-lactamase-producing enterobacter cloacae isolated from patients' samples in our hospital,and all of them possess ampC gene of DHA-1 type.