To characterize the genetic determinants responsible for extended-spectrum cephalosporin (ESC) resistance of d-tartrate-positive Salmonella enterica subsp. enterica serovar Paratyphi B (serovar Paratyphi B dT) strains that have emerged in poultry and humans in Belgium during 200810. The ESC resistance genes among non-redundant serovar Paratyphi B dT strains were determined using PCR and sequencing. ESC phenotypes were horizontally transferred by conjugation. Extended-spectrum -lactamase (ESBL)- or AmpC-carrying plasmids were typed by PCR-based replicon typing, plasmid multilocus sequence typing and restriction fragment length polymorphism. The genetic relationship of ESC-resistant strains was assessed by XbaI PFGE and multilocus sequence typing. Since 2008, the proportion of serovar Paratyphi B dT strains from broiler origin has increased significantly to reach 36.5 in 2010. Among 95 non-duplicate serovar Paratyphi B dT strains, 35 were resistant to ESCs. At the same time, a few ESC-resistant serovar Paratyphi B dT strains from humans were also detected in Belgium. The most prevalent ESBL gene, bla(CTX-M-1), and the AmpC cephalosporinase gene bla(CMY-2) were identified on various conjugative IncI1 plasmids of different sequence types and with different additional non--lactam phenotypes. Interestingly, the bla(CTX-M-2) gene was located on large multireplicon IncHI2/P plasmids. In addition, highly ESC-resistant strains contained both the ESBL CTX-M-2 and the AmpC CMY-2 encoded by the IncHI2/P and IncI1 plasmids, respectively. All ESC-resistant serovar Paratyphi B dT strains belonged to sequence type 28 and showed the common PFGE pattern X8, as well as the chromosomal class 2 integron cassette array dfrA1-sat2-aadA1 previously described in the European poultry-associated serovar Paratyphi B dT clonal population. This study showed that the clonal population of multidrug-resistant serovar Paratyphi B dT, persisting in broilers in Belgium for the last decade, recently acquired various plasmid-borne ESC resistance determinants, constituting a major concern for public health. Further surveillance programmes and research are an absolute necessity to understand their epidemiology and to propose interventions to limit the spread of ESC- and multidrug-resistant Salmonella spp.