Plasmid-mediated quinolone resistance (PMQR) in Enterobacteriaceae is related to Qnr-like proteins, and QnrB had not been identified in Europe prior to this study. This study aimed to determine the prevalence of QnrB in extended-spectrum β-lactamase (ESBL)-producing enterobacterial isolates (previously tested for QnrA and QnrS) from a French hospital. A total of 186 ESBL-producing enterobacterial isolates were collected from Bicêtre Hospital (a suburb of Paris, France) from January to June 2005 and screened for qnrB via PCR. One Enterobacter cloacae isolate (S1), recovered from the ascites of a 2.5-year-old child, was positive for both qnrB and qnrS1. Conjugation/transformation experiments, plasmid analysis, MIC testing, and gene sequencing were conducted. Sequencing revealed the qnrB variant was QnrB4, with perfect nucleotide identity to the qnrB4 reported in a U.S. E. coli isolate. QnrB4 was located on a 160-kb plasmid (pS1B), and its genetic environment was flanked by a psp operon (5’ end) and a sap operon (3’ end), showing 87% and 80% amino acid identity to corresponding E. coli K-12 proteins, respectively. The isolate also produced ESBL SHV-12, penicillinases TEM-1 and LAP-1, and had a gyrA (S83F) mutation. MIC results indicated QnrB4 and QnrS1 each mediated reduced susceptibility to quinolones/fluoroquinolones. This is the first report of a QnrB-like determinant in Europe and the first case of coexpression of two Qnr-like determinants (QnrB4 and QnrS1) in a single clinical isolate. The findings underline that plasmid-mediated quinolone resistance determinants may accumulate in enterobacterial clinical isolates, potentially further increasing quinolone resistance.