Background and Objective: Klebsiella pneumoniae is one of the most important causative agents both in form of hospital acquired and community-acquired infections. This bacterium is one of the most prevalent pathogens that is isolated from hospitals and is associated with high mortality rates. The uprising trend of multi drug resistance among Klebsiella pneumoniae has limited the treatment options. The objective of this study was to detect Metallo-beta-Lactamases, Extended-spectrum beta-lactamases (ESBLs) and outer membrane porins among Klebsiella pneumoniae strains isolated from hospitalized patients in Taleghani and Mofid hospitals. Materials and Methods: This cross-sectional study was performed on 100 Klebsiella pneumoniae isolates from 2012 to 2013. Antibiotic susceptibility tests were performed via Kirby-Bauer disc diffusion and Broth Microdilution methods according to CLSI guidelines. Metallo-beta-Lactamases, Extended-spectrum beta-lactamases (ESBLs) producing strains were detected by phenotypic confirmatory test and Combination Disk Diffusion Test (CDDT), respectively. The blaAIM, blaSPM, blaDIM, blaIMP, blaVIM ، blaTEM، blaSHV and blaCTX-M genes were detected using PCR and sequencing method. The outer membrane porins including OmpK35 and OmpK36 were analysed throughSDS-PAGE, PCR and sequencing methods. Results: Out of 100 K. pneumoniae isolates, 48 (48%) and 3(3%) were ESBL and MBL positive, respectively. The presence of blaTEM-1, blaSHV and blaCTX-M-15 was detected in 24 (50%), 30(62.5%) and 28 (58.33%) isolates respectively, while other genes were not detected. Outer Membrane Porins, OmpK35, was detected among 30 (62.5%) of 48 ESBL-producing isolates while OmpK36 was found in 35(72.91%) of 48 ESBL-producing isolates. In this study, Fosfomycin and Tigecycline were more effective than other antibiotics. 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