Antimicrobial drugs are widely used in poultry industry as growth promoters or to control infectious diseases. However, this practice is reported to have caused high resistance to antimicrobial drugs in normal chicken flora and pathogens. Antimicrobial resistance to Escherichia coli (E. coli) from chicken has been mainly reported in normal flora, but rare in pathogenic organism in Korea, recently. Therefore, this study was conducted to investigate prevalence of antimicrobials resistance, transfer of R plasmid, and association between antimicrobial drug resistance and O serotype of 203 pathogenic E. coli from poultry in Korea during the period from April 2003 to December 2005. These isolates showed a high resistance to tetracycline (Tc, 93.6%), nalidixic acid (Na, 92.6%), streptomycin (Sm, 81.8%), ampicillin (Ap, 77.3%), ciprofloxacin (Ci, 70.9%), sulfisoxazole (Su, 66.5%), and trimethoprim (Tp, 58.1%). Two hundred-one (99.0%) of the isolates were resistant to one or more drugs. They showed 57 different resistant patterns, and the most prevalent resistant pattern among them was Tc, Sin, Su, Ap, Tp, Ci, Na. Sixty-eight (33.8%) of the isolates transferred all or a part of their antimicrobial resistant pattern to the recipient strain by R plasmid. The most common antimicrobial resistant pattern was Tc, Sm, Su, Ap, Tp, Ci, Na in serotype O78, O88 and O15, respectively. These results exhibit high individual and multiple resistance to antimicrobials of pathogenic E. coli from poultry in Korea. They also suggest the needs for surveillance to monitor antimicrobial resistance in pathogenic bacteria that can be potentially transmitted to humans from food animals and to regulate the abuse of antimicrobials on food-producing animals in Korea.