Pseudomonas aeruginosa(P.aeruginosa) is one of the most common gram-negative pathogens associated with nosocomial infections, which are often difficult to treat because of the resistance of the bacterium against multiple antirnicrobials.Integron is a gene capture system that can spread drug resistant genes among bacteria.The aim of this study was to explore and compare the DNA structures of the class 1 integrons in 90 samples of P.aeruginosa isolated during two periods of time, namely 1992-1996 and 2005-2007.Polymerase chain reaction (PCR) and Long PCR were performed to amplify the class 1 integrons and the resistance cassettes carried on them.PCR products were sequenced and analyzed.Class 1 integrons detected in the samples from the years of 1992-1996 were 1734 bp in length and contained in average 1.9 resistance cassettes.