The biological synthesis of palladium nanoparticle (BioPd) by S. oneidensis MR-1 and its ability to reduce 2-chloronitrobenzene (2-CNB) were investigated. The results showed that BioPd reduced 2-CNB through cooperation with S. oneidensis MR-1, and heavily depended on the quinone dehydrogenase CymA in S. oneidensis MR-1. The reduction products included in nitrobenzene, chloroaniline and aniline, and aniline was the final product, indicating that the synergistically catalytic system could achieve dechlorination and nitro-reduction simultaneously. The reduction of 2-CNB could be described as the second-order kinetics.