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Diffusible signal factor (DSF) represents a family of widely conserved quorum sensing (QS) signals involved in the regulation of virulence factor production in many Gram-negative bacterial pathogens. Quorum quenching, which disrupts QS either by degradation of QS signals or interference of signal generation or perception, is a promising strategy for prevention and control of QS-mediated bacterial infections. In this study, a novel DSF-degrading strain, HN-2, was isolated from contaminated soil and identified as <i>Cupriavidus</i> sp. The isolate exhibited superior DSF degradation activity and completely degraded 2 mmol&#183;L^&#8722;1 of DSF within 24 h. Analysis of the degradation products of DSF by gas chromatography&#8722;mass spectrometry led to the identification of trans-2-decenoic acid methyl ester as the main intermediate product, suggesting that DSF could be degraded by oxidation and hydroxylation. Moreover, this study presents for the first time, evidence that <i>Cupriavidus</i> sp. can reduce the black rot disease caused by <i>Xanthomonas campestris</i> pv. <i>campestris</i> (<i>Xcc</i>). Application of the HN-2 strain as a biocontrol agent could substantially reduce the disease severity. These findings reveal the biochemical basis of a highly efficient DSF-degrading bacterial isolate and present a useful agent for controlling infectious diseases caused by DSF-dependent bacterial pathogens.