Effects　of　potassium　alkalis　and　sodium　alkalis　on　the　dechlorination　of　o-chlorophenol　(o-CP)　in　supercritical　water　(SCW)　were　studied　in　this　paper　under　the　conditions　of　450　degrees　C　and　25　MPa.　Experimental　results　indicated　that　the　dechlorination　of　o-CP　can　be　accelerated　significantly　by　all　alkalis　investigated.　The　dechlorination　of　o-CP　proceeded　mainly　via　two　pathways:　hydrodechlorination　and　hydrolysis.　Both　of　the　two　pathways　can　be　promoted　by　alkalis,　and　the　dechlorination　of　o-CP　can　be　accelerated　by　both　the　cations　and　hydroxide　ion　dissociated　from　alkalis.　The　overall　dechlorination　of　o-CP　can　be　accelerated　by　cations　via　promoting　the　hydrodechlorination　pathway,　while,　hydroxide　ion　via　promoting　the　hydrolysis　pathway.　In　addition,　the　hydrodechlorination　can　be　accelerated　faster　by　sodium　alkalis　than　that　by　potassium　ones,　while,　the　hydrolysis　can　be　promoted　faster　by　potassium　alkalis.　This　difference　may　be　caused　by　the　different　charge　density　between　potassium　ion　and　sodium　ion,　and　the　different　solubility　and　dissociation　constant　between　potassium　alkalis　and　sodium　alkalis　in　SCW.　Dechlorination　of　o-CP　with　addition　of　alkalis　prior　to　supercritical　water　oxidation　(SCWO)　process　not　only　can　avoid　the　reactor　corrosion　caused　by　the　generated　hydrochloric　acid　in　direct　SCWO　of　o-CP,　but　also　can　reduce　the　formation　of　toxic　chlorinated　byproducts　compared　with　direct　SCWO　process　or　SCWO　of　o-CP　with　addition　of　alkali.　(c)　2006　Elsevier　Ltd.　All　rights　reserved.