The present study describes integron mediated multiple antibiotic resistance in extended-spectrum β-lactamase producing clinical isolates of Klebsiella pneumoniae. One hundred and four clinical isolates of K. pneumoniae from two Iranian hospitals were screened for extended-spectrum β-lactamase production and susceptibility of the extended-spectrum β-lactamase producing isolates was determined to 17 antibiotics by disc diffusion. Presence of integron classes 1, 2 and 3 was detected by PCR and integrase specific primers. Isolates harboring class 1 integron were then screened for variable regions using PCR. Fifty isolates (48%) produced extended-spectrum β-lactamases among which, 22 (44%) harbored class 1, 3 (6%) carried class 2 and none contained class 3 integons. Integron carriage was significantly associated with higher rates of multiple antibiotic resistance in extended-spectrum β-lactamase producing clinical isolates of K. pneumoniae. Integron harboring isolates were more resistant to aztreonam (51.3%), ceftazidime (42.6%), cefotaxime (43.3%), cefepime (24.6%), kanamycin (43.2%), tobramycin (30.7%), norfloxcacin (32%) and spectinomycin (25.6%) compared to the organisms without integrons. On the other hand, resistance to nitrofurantoin and streptomycin was significantly higher among the integron negative isolates. PCR amplification of class1 integron variable regions revealed 9 different sized DNA fragments and isolates with similar profiles for class 1 integron variable regions showed the same antibiotic resistance phenotypes.