Abstract: Antimicrobial agents are used extremely in order to reducing the enormous losses caused by Escherichia coli infections (Colibacillosis) in Iran poultry industry. In this investigation, 200 Avian Pathogenic Escherichia coli (APEC) strains isolated from broiler chickens with Colisepticemia and examined for susceptibility to antimicrobials of veterinary and human significance. Multiple resistances to antibiotics were observed in all the isolates. The highest rate of resistance was against Nalidixic acid (98), Lincomycin (97.5), Erythromycin (97), Oxytetracycline (92), Chloretracycline (92), Flumequine (90), Doxycycline (80), Difloxacin (80), Neomycin (62), Streptomycin (62), Trimethoprim-Sulphamethoxazonle (60), Kanamycin (60), Enrofloxacin (60), Norfloxacin (55), Ciprofloxacin (50), Chloramphenicol (49), Furazolidone (45.5) and Nitrofurantoin (45%). Resistance to Gentamicin, Ceftifur and Fosbac were not observed and to Amikacin, Cefazolin, Colistin, Lincospectin and also Florfenicol were low. This study showed resistance rate against the antibiotics that are commonly used in poultry is very high but against them that are only used in human or less frequently used in poultry is significantly low. This study also showed that the prevalence of Quinolone Resistant Escherichia coli (QREC) are very high in broiler farms in Tabriz province. The high presence of OREC from broiler chickens probably id due to overuse of enrofloxacin in these farms for therapeutic purposes.