In　radiation　research　facility,　where　heat　and　radiation　are　two　crucial　factors　inducing　material　degradation,　highly　stable　materials　are　required.　In　the　present　work,　various　properties　of　poly(ether　ether　ketone)　(PEEK)　exposed　to　heat　and　gamma　rays　in　air　are　instrumentally　investigated.　If　PEEK　is　aged　by　heat　and　gamma　irradiation　in　air,　chemical　bond　scission,　oxidation,　crosslinking,　and　char　formation　occur　as　competing　mechanisms.　The　temperature　plays　a　decisive　role　in　degradation,　while　the　irradiation　accelerates　it.　The　mechanical　properties　deteriorate　much　earlier　than　the　dielectric　properties　with　the　progress　of　aging.　This　means　that　the　mechanical　properties　can　be　an　important　condition　monitoring　factor　compared　to　the　dielectric　properties　for　PEEK-insulated　apparatus　or　cables.　If　PEEK　is　aged　severely,　its　electrical　conductivity　increases　dramatically,　whereas　both　real　and　imaginary　parts　of　complex　dielectric　permittivity　decrease,　showing　a　marked　contrast　to　many　industrially　important　polymeric　insulating　materials.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.