Resent studies have reported increased isolation of extended-spectrum $eta-lactamase$ (ESBL) producing strains at several hospital in Korea. We studied to investigate the isolation rates of ESBL strains from clinical isolates of Klebsiella pneumoniae and to characterize differences in types using analyses of genotyping and antibiotic susceptibility test. Antibiotic susceptibility test with confirmation of ESBL by double disk synergy test was performed on the 54 ESBL strains of Klebsiella pneumoniae from a hospital in Busan. Transfer of resistant gene in ESBL strains resistant to 3rd generated antibiotics was confirmed by transconjugation test using E. coli $RG176^{nal(r)}$. blaTEM, blaSHV, blaCTX-M genes were detected by PCR. ESBL producing strains had 100% of resistant rate to ampicillin, azteronam, cefazolin, cefepime and ceftriaxone ($eta-lactam$ antibiotics). Forty strains of bla TEM$(74\%)$, 41 strains of bla SHV $(76\%)$, 23 strains of bla CTX-M $(43\%)$ were found, respectively. The strains had one or more genes. They had high resistant rates to $eta-lactam$ antibiotics including cephalosporin. The resistant rates of strains with multiple resistant genes were higher than those of strains with single resistant gene.