TEM- and SHV-derived extended-spectrum beta-lactamases (ESBLs) producing Enterobacteriaceae have been reported from throughout the world, but there has been limited data for the molecular characterization of these enzymes in Turkey. The aim of this study was to investigate and to type the TEM- and SHV-derived ESBLs in 63 ESBL-producing clinical isolates of Enterobacteriaceae, and it included further analysis; transfer experiments, isoelectric focusing, PCR, PCR-restriction fragment length polymorphism, and DNA sequencing. According to PCR results the transconjugant strains included 52.7% TEM, 74.3% SHV, and 32.4% of both the TEM and SHV genes. Using PCR/Nhel restriction analysis, 45 of the 46 ESBL detected in transconjugants were determined to be SHV-derived. DNA sequencing was performed for the identification of TEM- and SHV-derived ESBLs for 18 selected transconjugants. SHV-2, SHV-5, and SHV-12 were detected in five, seven, and five samples, respectively. This is the first description of SHV-12 in Turkey.