Introduction: One of the enzymes that is produced by Gram negative bacteria is Extended spectrum-β-lactamases (ESBLs) which was first described in the 1980s. This study aims at identifying three common genes (blaTEM, blaSHV and blaCTX-M) in Klebsiella pneumoniae isolated from patients in Arak, Iran. Methods: A total number of 112 isolates were selected during 2012-2013. To identify phenotypic specifications, Combination Disk Method based on CLSI guidelines. The ESBL’s genotype was analyzed by multiplex PCR and DNA sequencing. Results: Among 10 examined antibiotics, the most resistant and susceptible antibiotics were ampicillin and imipenem, respectively. The phenotypic determination of ESBL showed that 46.42% of isolates produced ESBL. The molecular survey of genes showed that 35.89% had CTX-M, 5.12% had both CTX-M and TEM and 2.56% had TEM, SHV, CTX-M. Conclusion: According to the findings, the high prevalence (73.07%) of ESBL producing K. pneumoniae was observed with a new pattern of blaCTX-M distribution differed from other countries. پرونده مقاله