Background: Plasmid mediated quinolone resistance (PMQR) has been shown to play an important role in resistance not only to quinolones, but also β-lactams and aminoglycosides. In fact, qnr genes are frequently carried along with β-lactamase determinants on the same plasmids. We studied the prevalence of qnrA, qnrB, qnrS and aac(6’)-Ib-cr genes among quinolone and cephalosporin resistant clinical isolates of Klebsiella pneumoniae (K. pneumoniae), as well as the association between PMQR genes with resistance to quinolones, cephalosporins and aminoglycosides.Methods: The study was conducted on 79 K. pneumoniae clinical isolates collected from Imam Hussein hospital in Tehran between July 2010 and January 2011, based on their resistance to quinilones and cephalosporins. Antibacterial susceptibility was determined to 15 antibiotics by disc diffusion. Presence of qnrA, qnrB, qnrS and aac(6’)-Ib-cr genes were investigated using specific primers and PCR.Results: Of the 79 K. pneumoniae isolates, 47 (59.5%) carried the PMQR determinants. Among these, 42 (89.4%) carried aac(6’)-Ib-cr of which, 21 (50%) also harbored qnrB. Three isolates carried qnrB alone, two (4.2%) harbored qnrS and none had qnrA. Resistance to aminoglycosides and cephalosporins was significantly higher in the isolates carrying both qnrB and aac(6’)-Ib-cr genes compared to aac(6’)-Ib-cr alone.Conclusion: This study showed a high prevalence of aac(6’)-Ib-cr and qnrB genes among the Iranian K. pneumoniae clinical isolates as well as co-carriage of the two genes. There was a significant association between qnrB gene carriage and resistance to quinolones, cephalosporins, and aminoglycosides.