As　an　emerging　advanced　oxidation　technology,　ultraviolet/peracetic　acid　(UV/PAA)　shows　great　potential　in　removing　pharmaceuticals　and　personal　care　products　(PPCPs)　in　the　field　of　wastewater　treatment.　In　this　work,　ibuprofen　(IBP)　was　chosen　as　the　contaminant　to　study　the　degradation　effects　and　PAA　activation　mechanisms　by　UV　irradiation.　The　experimental　results　showed　that　UV/PAA　had　an　excellent　degradation　efficiency　(99.22　%)　of　IBP　after　15　min　reaction,　and　the　synergistic　effect　between　UV　and　PAA　was　also　observed.　Increasing　the　dosage　of　PAA　caused　the　increase　in　IBP　degradation　reaction　rate.　Under　acidic　conditions,　the　increase　in　pH　values　increased　the　degradation　reaction　rate,　whereas　the　opposite　was　true　in　alkaline　conditions.　In　addition,　the　coexisting　substrates　(e.g.,　NO3-,　CO32-,　Ca2+,　and　HA)　could　exert　inhibition　on　the　degradation.　Quenching　experiments　were　carried　out　using　various　quenchers　to　identify　reactive　oxygen　species　(ROSs)　in　the　system.　The　results　demonstrated　that　·OH　and　carbon　centered　radicals　(R-C·)　played　a　dominant　part　in　the　degradation,　and　the　contribution　of　CH3C(O)OO·,·O2-,　CH3C(O)O·,　·OH,　and　direct　photolysis　were　estimated　to　be　29.9　%,　26.9　%,　21.5　%,　14.5　%,　and　7.2　%,　respectively.　The　results　of　IBP　intermediates　identification　indicated　that　the　degradation　process　was　mainly　related　to　its　side　chain　decarboxylation,　oxidative　dehydrogenation,　demethylation,　and　the　oxidation　of　the　aromatic　ring.　Furthermore,　Toxicity　Estimation　Software　Tool　(T.E.S.T.)　and　ECOSAR　were　applied　to　evaluate　the　toxicity　of　the　intermediate　products　was　further　evaluated.　This　study　enriched　the　understanding　of　the　PAA　activation　mechanism　by　UV　involved,　and　improved　the　theory　and　technology　of　removing　PPCPs　by　UV/PAA　process.　©　2023　The　Institution　of　Chemical　Engineers