This study is a review of different causes of bacterial resistantepecially production of B-lactamase enzyme, its classification, methodof detection of extended spectrum B-lactamases and type of anti-microbial susceptibility tests.We collect 144 clinical isolate of klebsiella from patient in Kasr El-Aini Hospitals, we find that prevalence of ESBLs producingstrain of klebsiella was (20.8%) 30 isolates detected by both DDS27(90%) and E-test 22 (73%) which include 3 isolates was detectednegative by DDS.We find that DDS test can be used in routine investigation todetect ESBLs producing isolates.