Objective(s) Different types of extended spectrum beta-lactamases (ESBLs) are encountered in the clinical settings worldwide. There are a few studies regarding the prevalence of ESBL genes among Klebsiella pneumoniae isolates at Tehran especially those of blaPER and blaCTX. The aim of this study was to determine the prevalence of blaSHV, blaTEM ,blaPER and blaCTX genes among clinical K. pneumoniae of different hospitals in Tehran. Materials and Methods Two hundred isolates of K. pneumoniae were received from different clinical specimens. The susceptibility of the isolates to 10 different antibiotics was examined by disk diffusion test. The MICs for ceftazidime were also determined using micro-broth dilution assay. Isolates showing MIC≥ 4 μg/ml for ceftazidime were screened for ESBL production by phenotypic confirmatory test (PCT) and subjected to PCR for studied genes. Variation among four amplified genes was evaluated using PCR-RFLP. Results By disk diffusion test, resistance to ceftazidime and cefotaxime were 34.7% and 33.5% respectively. However, all strains were susceptible to imipenem. Eighty isolates showed MICs≥ 4 μg/ml for ceftazidime of which 77 (96%) were positive for ESBL in PCT. The prevalence of blaSHV, blaCTX-M, blaTEM and blaPER among these isolates were 26%, 24.5%, 18% and 7.5%, respectively. No variation was detected in the genes by PCR-RFLP. Conclusion As far as we know this is the first report of the blaPER-1 in K. pneumoniae in Iran. The blaCTX-M was the second most common gene detected among the ESBL positive isolates of K. pneumoniae. For rapid identification of ESBL producing isolates it was recommended that clinical laboratories adopt simple test based on CLSI recommendation for confirming ESBL production in enterobacterial species.