We　have　attempted　to　clarify　the　fomation　mechanism　for　long－1ived　and　highly　reactive　oxygen・centered gas－phase　radicals　from　the　combustion　smoke　of　polymethyl　methacrylate　and　polypropylene　using　the　ESR spin-trapPing　technique， The　combustion　smoke　was　bubble6through　benzene　without　pheny1－N－t－butylnitroれe（PBN）as　a　spin　trap，and　then　PBN　was　added　to　it　after　a　certain　delay　time・The　gas・phase　radi￠als　from　combustion　were　much longer－lived　in　the　solution　in　spite　of　its　high　reactivity　than　that　from　cigarette　smoke， In　addition，the　combustion　smoke　was　trapped　with　a　CC13F　solution　of　PBN　at一78℃，and　their　ESR　spectra were　observed　under　elevating　temperature．The　ESR　signal　increased　remarkably　at－30～一40℃，suggesting any　possibility　for　the　decomposition　of　such　a　meta－stable　oxygen・containing　compound　as　a　trioxide，and　this behavior　is　different　from　that　of　cigarette　smoke， From　the　above　results　we　can　suggest　that　long・1ived　and　highly　reactive　oxygen・centered　gas－phase　radicals should　be　produced　from　combustion　smoke　by　the　mechanism　involving　the　formation　and　decomposition　of　such a　meta－stable　oxygen－containing　compound　as　a trioxide．