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Abstract: Catalytic dechlorination of para-nitrochlorobenzene (p-NCB) by Ni/Fe (nickel/iron) bimetallic nanoparticles was carried out. The catalytic reduction and dechlorination reaction was believed to take place on the surface site of the nanoscale catalysts. In the reaction, Ni plays a role of catalyst decreasing activation energy of hydrogenolysis of C–Cl bonds and the Fe was corroded to produce hydrogen gas. 100% dechlorination efficiency was achieved for particles with 2.0% Ni, in contrast, just 51% chlorine was obtained for particles with 0.5% Ni at the Ni/Fe nanoparticles mass concentration of 6 g l−1 used after 300 min reaction. The p-NCB was first adsorbed by nanoparticles completely then quickly reduced to p-chloroaniline (p-CAN) and aniline (AN), and p-CAN was detected as an intermediate. As expected, with the Ni/Fe addition and the Ni loading percentage over Fe increasing, the temperature going up, and the pH decreasing, the dechlorination efficiency increased. The Ni/Fe catalytic reductants showed prominent activity to the reductive catalytic dechlorination of p-NCB at ambient temperature and pressure as well as high removal efficiency of p-NCB and p-CAN in agricultural pesticide wastewater, therefore, they could be good choices for remediation of contaminated groundwater. [Copyright &y& Elsevier]