9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide　(DOPO)　was　immobilized　onto　the　surface　of　titanium　dioxide　(TiO2)　nanoparticles　in　supercritical　carbon　dioxide.　The　DOPO　immobilized　TiO2　was　characterized　by　UV-visible　spectroscopy,　magic　angle　spinning　nuclear　magnetic　resonance　and　thermogravimetric　analysis.　Cone　calorimeter　was　used　to　characterize　the　flame　retardancy　properties.　By　incorporating　the　DOPO-immobilized　TiO2　nanoparticles　(TiO2-g-DOPO)　(5%)　into　the　polyurethane　matrix,　the　heat　release　rate　and　total　heat　release　decrease.　SEM　observation　were　performed　on　the　combustion　residue　chars　after　cone　calorimeter　test.　It　is　found　the　char　layer　is　compact　for　polyurethane　with　TiO2-g-DOPO.　Apparent　activation　energies　of　the　polymer　composites　were　estimated　via　Ozawa　method.　It　is　found　that　the　incorporation　of　TiO2-g-DOPO　improves　activation　energies.　Based　on　the　results,　it　is　speculated　that　TiO2-g-DOPO　could　inhibit　the　degradation　of　polyurethane　and　catalyze　the　formation　of　carbonaceous　char　on　the　surface.　Thus,　flame　retardancy　properties　of　polyurethane　are　improved.　©　2019,　Editorial　Board　of　Polymer　Materials　Science　&　Engineering.　All　right　reserved.