ESBLs are plasmid mediated enzymes capable of hydrolyzing the B-lactam antibiotics including penicillins and broad spectrum cephalosporins. ESBL dissemination has been reported worldwide. Since the detection of the first TEM-1 plasmid-encoded enzyme in Escherichia coli, more than 200 types of ESBLS have been detected worldwide. Specific ESBL variant can be distinct to a certain country or a region. The aim of this study was to detect ESBLs in clinical isolates of E. coli and to characterize these as TEM or SHV using PCR. A total of ninety eight isolates of E. coli recovered from various clinical samples of patients attending Sultan Qaboos University Hospital were collected during a 4 month (Nov-Feb) period in 2008. Isolates were screened for ESBL production using the Clinical laboratory Standards Institute (CLSI) recommended disk diffusion method. The screen positive isolates were subjected to phenotypic confirmatory test as recommended by CLSI. Characterization of the ESBLs produced by the isolates as TEM and SHV was undertaken using PCR and specific primers. A total of 17 (17.3%) isolates were confirmed to be ESBL producers by the phenotypic confirmatory test. In five of these 17 isolates the ESBLs could be confirmed as TEM. None of the isolates harbored the SHV type of ESBL, A large majority of ESBL producers were isolated from urine (70.6%). A larger percentage of isolates recovered from hospitalized patients (-18.5 %) were positive for ESBL as compared to the isolates recovered from outdoor patients (-15.2 %). All the isolates were susceptible to imipenem. Resistance to gentamicin (53% versus 7.4%) and ciprofloxacin (88.2% versus18.5%) was more common among ESBL positive isolates than in ESBL negative isolates. Cefotaxime proved to be a better substrate than ceftazidime since the former detected 17 while the later detected 15 isolates as ESBL producers.