In　this　study,　we　have　investigated　the　degradation　and　primary　radiolytic　degradation　mechanism　of　4-tert-octylphenol　(4-t-OP)　by　using　of　electron　beam　(EB)　-irradiation.　The　results　show　that　at　an　absorbed　dose　of　10　kGy　and　an　initial　concentration　of　25　mg.L-1,　the　degradation　of　4-t-OP　in　a　methanol/water　reduction　system　is　higher　than　in　a　acetonitrile/water　oxidation　system　by　19.4%　and　higher　than　in　an　acetone/water　system　by　26.8%,　which　is　due　to　both　of　center　dot　OH　and　e(aq)(-)　playing　an　important　role　in　the　decomposition　of　4-t-OP,　although　the　latter　is　more　effective.　The　degradation　rate　of　4-t-OP　will　decrease　with　increment　of　absorbed　dose　in　a　methanol/water　solution,　and　increase　with　decrement　of　initial　concentration　at　a　constant　absorbed　dose.　The　degradation　efficiency　will　also　decrease　with　the　addition　of　anions　and　H2O2　into　the　solution.　A　system　saturated　with　N-2　will　make　an　increment　in　the　degradation　of　4-t-OP.　The　pH　value　of　solution　has　been　also　found　to　affect　the　degradation　efficiency,　while　the　degradation　is　more　efficient　in　alkaline　conditions.　Finally,　the　initial　products　involved　in　degradation　reaction　have　been　determined　to　be　ethylbenzene,　styrene,　bicyclo[4.2.0]octa-1,3,5-triene,　2,2,4-trimethylpentane　and　p-tert-butyl-phenol,　which　may　arise　from　e(aq)(-)　attack　at　the　position　of　the　alkyl　side　chain　of　4-t-OP　molecule.　The　results　have　been　revealed　that　EB　irradiation　is　a　promising　method　for　degradation　of　4-t-OP,　and　e(aq)(-)　may　be　main　reactive　species　to　attack　at　the　position　of　the　alkyl　side　chain　of　4-t-OP.