Nanoscale zero-valent iron (NZVI) particles were synthesized in the laboratory and used to investigate the reduction kinetics and degradation mechanisms of hexachlorobenzene (HCB) and the environmental effects. The rapid degradation of HCB by NZVI follows pseudo-first-order kinetics. Increasing the dose of NZVI particles enhanced the dechlorination rates of HCB. With an increase in temperature, the degradation rate increases. The activation energy was determined to be 16.6 kJ mol(-1). The dechlorination rate constants of HCB linearly increased from 0.052 to 0.12 h(-1) with decreasing aqueous pH values from 9.2 to 3.2. The dehalogenation of HCB with NZVI is favorable under acid conditions. The degradation kinetics and efficiency increased with increasing water content in solutions, indicating that hydrogen ion was also one of the driving forces of reaction. The stepwise dechlorination pathway of HCB with NZVI was the dominant reaction. These findings indicate high temperature and acid conditions are beneficial to the catalytic dechlorination of polychlorinated benzenes with NZVI and it potential application into the environment. Crown Copyright (c) 2010 Published by Elsevier B.V. All rights reserved.