Two major porins that facilitate diffusion of antimicrobials have been described in Klebsiella pneumoniae (Omp35 and Omp36). Our study was carried out to detect the effect of porin loss among Extended Spectrum β-Lactamase (ESBL) and AmpC β-Lactamase producing K. pneumoniae clinical isolates on increasing the minimum inhibitory concentration of imipenem. Methods: In our study 91 K.pneumoniae clinical isolates that were suspected to be ESBLs producers by the initial screening test were subjected to phenotypic analysis including confirmatory tests for ESBLs and AmpC β-lactamases production according to the guidelines of the Clinical and Laboratory Standards Institute. Further genotypic analysis of Omp35 and Omp36 genes were done to all 91 K.pneumoniae isolates by reverse transcriptase polymerase chain reaction (RT-PCR), whereas sodium dodecyl sulfate –polyacrylamide gel electrophoresis (SDS-PAGE) was done only for 38 isolates to be compared with the results of RT-PCR.Conclusion: Loss of both Omp35,Omp36 enhanced the resistance to cefoxitin and ceftazidime among ESBL producing isolates. Increase of IMI MIC was detected among AmpC producing K.pneumoniae isolates with loss of both porins.