Colibacillosis is an importantbacterial disease of poultry with huge financial losses. Due to the importance of bacterial resistance, this study has been undertaken to determine antimicrobial sensitivity of E.coli isolates in Urmia. During 2006-2011, antimicrobial susceptibility tests of 1100 E.coli isolates from Urmia broiler farms were collected and resistant patterns were analyzed. The antibiotics include ampicillin, enrofloxacin, colistin, sulfamethoxazole+trimethoprim (co-trimoxazole®), erythromycin, flumequine, florfenicol, lincomycin+spectinomycin (linco-spectin®), neomycin, oxytetracycline, sulfadiazine+trimethoprim (sultrim®), tiamulin, tylosinandtetracycline. The findings of this study show alteration in susceptibility pattern during 6 years. For the first three years, most of the isolates were resistant to tylosin 2006(99.6%), 2007(99.6%) and 2008(98.75%) and most of them were sensitive to florfenicol 2006(86.4%), 2007 (62.8%) and 2008 (62.08%). From 2009 to 2011 different results were recorded. The highest rate of résistance observed to tetracycline (100%), erythromycin (97.83%) and tetracycline (100%), respectively while lincomycin+spectinomycin was more sensitive agent than the others 2009(77.91%), 2010(76.75%) and 2011(75.83%). More comprehensive study should be carried out as a national plan comparing antibacterial sensitivity test of all provinces in order to find out an overview of antimicrobial susceptibility pattern in the country.

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