About 408 Escherichia coli were isolated from sick farm animals and pets during 2003-2006. Of these isolates, four strains showed resistance to third-generation cephalosporins. The bla(CTX-M-14) gene was encountered in three E. coli strains, each of which were isolated from two cows and a dog, respectively, and bla(CTX-M-15) was identified in an E. coli isolated from a pig. All bla(CTX-M) genes were found to be transferred. The pulsed-field gel electrophoresis pattern indicated that the CTX-M-type beta-lactamase-producing E. coli isolates were genetically diverse. This study shows the emergence of CTX-M-type beta-lactamase-producing E. coli in animals for the first time in Korea. Study results suggest the need for awareness and comprehensive monitoring of extended-spectrum beta-lactamases in animals because gene transfer can occur between animals as well as humans.