Objectives: To elucidate the prevalence of extended - spectrum β - lactamases among Enterobacter cloacae and to investigate the genotypes of ESBLs producers in Beijing Chaoyang Hospital. Methods: Phenotype screening test was performed to detect the 58 strains of Enterobacter cloacae resistant to the third - generation cephalosporins or aztreonam. Standard agar dilution method, isoelectric focusing, PCR amplification, gene clone and DNA sequencings were preformed in 20 clinical isolates which were confirmed by phenotype screening test. Results: Results of phenotype screening test showed 20 strains (34.48%) produced ESBLs enzymes. The susceptible rates to cefoxitin, cefepime piperacillin/tazobactam and cefotaxime/sulbactum was 100%, 37.5%, 50% and 87.5%, respectively. ESBLs puls AmpC beta - lactamase - producers were only susceptible to impenem. DNA sequencing of amplicons of 14 strains revealed ESBLs of SHV - 2, SHV - 2a, SHV - 12, CTX - M - 14 and CTX - M - 22, respectively. The other six strains produced unidentified enzymes with pI 7.89, 8.0, and 8.57 which were inhibited by clavulanic acid. Conclusion: ESBLs are one of the important drug - resistant mechanisms of Enterobacter cloacae.