Pentachlorophenol　(PCP)　is　a　highly　toxic　pollutant.　The　effect　of　nitrate　on　the　degradation　of　PCP　by　iron　nanoparticles　synthesized　was　investigated　using　the　chemical　reductive　method.　The　concentrations　of　PCP　and　chloride　in　solutions　with　different　concentrations　of　nitrate　were　measured　during　the　treatment　process.　The　intermediate　and　final　products　from　the　PCP　and　iron　nanoparticles　were　also　analyzed.　The　results　show　that　when　the　initial　concentration　of　PCP　is　0.1　mmol　·　L-1,　NO3-　at　≤　1　mmol　·　L-1　does　not　affect　the　degradation　of　PCP.　NO3-　at　2　mmol　·　L-1　slows　the　PCP　dechlorination　and　NO3-　at　≥　3　mmol　·　L-1　stops　the　PCP　dechlorination.　The　oxidized　intermediates　were　more　likely　with　NO3-.　The　iron　nanoparticles　are　transformed　to　Fe2O3/Fe3O4　and　FeOOH　with　and　not　with　NO3-.