Extended spectrum β-lactamase (ESBL) generated Enterobacteriaceae including Escherichia coli is responsible for resisting antibiotics, which is clinical problem. This study was performed to investigate the isolation rates of 111 strains having positive of VITEK ESBL test 111 ESBL-strains in each month and season and statistically to determine their patterns of antibiotic test. One hundred eleven ESBL-strains were collected among 1,688 strains of E. coli isolated from various clinical specimen of one general hospital in Busan during 2002 to 2003. Month rates of ESBL-strains were 0％ to 13.3％, while the seasonal rates were highest at autumns during two years. The resistance to ampicillin, cefazolin, azteronam, ceftriaxone, and cefepime were 100％ in 2002. In ampicillin and cefazolin the resistances were 100％ during the two years. There were significant differences of cefoxitin and piperacillin/tazobactam between the two years but not significant between specimens. Four groups were divided according to the pattern of resistance and then the highest group had 93∼100％ of the resistance to 8 drugs but not resistant to imipenem.