The　dechlorination　of　pentachlorophenol　(PCP)　using　nano-Fe　together　with　different　size　of　nano-Ni　particles　(30,　50,　80,　and　100　nm)　was　investigated.　The　results　indicated　that　nano-Ni　particles　could　improve　the　dechlorination　of　PCP.　The　X-ray　powder　diffraction　(XRD)　analysis　suggested　that　nano-Ni　particles　might　serve　as　catalyst　for　dechlorination.　The　decrease　of　nano-Ni　particle　size　resulted　in　the　increase　of　PCP　transformation　and　chloride　release.　The　accumulation　of　several　intermediates,　such　as　phenol.　2-chlorophenol,　3-chlorophenol　and　4-chlorophenol　indicated　the　probable　changes　of　the　reaction　pathway　for　PCP　dechlorination.　The　corrosion　products　of　Fe　were　detected　using　XRD　analysis.　In　the　system　without　nano-Ni　particles,　they　were　lepidocrocite　(gamma-FeOOH)　and　magnetite　(Fe3O4)　and/or　maghemite　(Fe2O3),　however,　in　the　systems　with　nano-Ni　particles,　they　were　still　magnetite/maghemite　but　no　lepidocrocite　existed.　The　size　of　nano-Ni　particles　might　affect　the　crystallization　of　corrosion　products　of　Fe,　but　did　not　affect　the　species　distribution　of　corrosion　products.　(C)　2010　Elsevier　B.V.　All　rights　reserved.