Background: Although Escherichia coli (E. coli)is a part of intestinal normal microflora of warm-blooded animals, includingpoultry, outbreaks occur in poultry raised below standard sanitation and duringthe course of respiratory or immunosuppressive diseases. Avian pathogenic E.coli (APEC) harbors several genes associated with virulence andpathogenicity. APEC strains are responsible for some diseases in poultryincluding colibacillosis, swollen head syndrome, yolk sac infection, omphalitisand coli granuloma. OBJECTIVES:  Theaim of this study was examination of the presence and frequency of threeimportant virulence genes in intestinal and extra-intestinal (liver) E. coliisolates from chicken of Khuzestan province in the southwest of Iran. METHODS:Totally 120 (60 intestinal and 60 liver) E. coli isolates were examinedby polymerase chain reaction (PCR) for the presence of aerobactin (iutA),temperature sensitive hemagglutinin (tsh) and fimbriae type 1 (fimH )genes.  RESULTS: The results showedthat tsh, iutA and fimH are respectively present in 78.3%, 70% and 61.7% ofliver isolates while in intestinal ones the frequency of these genes was 21.7%,41.7% and 41.7% respectively. The most prevalent genotypes in extra intestinaland intestinal isolates were tsh+fimH+iutA+ and tsh-fimH-iutA-respectively. CONCLUSIONS: It seems that these sets of virulence genes are significantly moreprevalent (P<0.05) in extra intestinal isolates and probably these genesplay an important role in the pathogenesis of APEC isolates in the southwest ofIran. Although these virulence genes were not present in all APEC isolates  their frequencies were high and using theproducts of these genes in vaccines may be effective in protecting againstinfections caused by this bacterium