The　degradation　characteristics　of　clopyralid　irradiated　by　electron　beam　(EB)　was　studied　in　aqueous　solutions.　The　effects　of　factors,　such　as　initial　clopyralid　concentrations,　addition　of　radicals　scavenger,　initial　solution　pH　and　addition　of　H(2)O(2),　were　investigated　on　clopyralid　degradation　efficiency　and　mechanism.　It　was　found　that　the　EB-radiolysis　was　an　effective　way　to　degrade　clopyralid　and　its　degradation　rate　decreased　with　the　increasing　of　substrate　concentration.　In　the　investigated　initial　concentrations　range　of　100-400　mg　L(-1),　the　radiolytic　degradation　of　clopyralid　followed　a　pseudo-first　kinetic　order.　The　results　from　addition　of　radicals　scavenger　indicated　that　both　(aEuro　cent)OH　and　e　(aq)　(-)　played　significant　roles　in　the　degradation　of　clopyralid.　Furthermore,　the　alkaline　condition　and　addition　of　H(2)O(2)　(＜　10　mM)　in　the　solution　also　slightly　enhanced　the　efficiency　of　clopyralid　degradation.　The　ion　chromatography　analysis　showed　that　some　organic　acids　(formic　acid,　acetic　acid　and　oxalic　acid)　were　formed,　while　the　completely　dechlorination　of　the　substrate　was　achieved　and　organic　nitrogen　was　recovered　in　the　form　of　ammonium　and　nitrate　ions　during　the　irradiation　process.