Extensive　application　of　epoxy　resins　(EPs)　is　highly　limited　by　their　intrinsic　flammability.　Combining　EPs　with　nanoparticles　and　phosphorus-nitrogen　flame　retardants　is　an　effective　approach　to　overcome　the　drawback.　In　this　work,　simultaneous　incorporation　of　octa-aminophenyl　polyhedral　oligomeric　silsesquioxanes　(OapPOSS)　and　polyphosphazene　into　EP　was　reported　for　the　first　time.　Significantly,　reduced　peak　of　heat　release　rate　and　UL-94 V-0　rating　were　achieved　by　tuning　suitable　ratios　of　polyphosphazene　and　OapPOSS　for　EP　composites.　During　combustion,　polyphosphazene　promoted　char　formation　and　released　nonflammable　gases　such　as　CO2,　NH3,　and　N2　to　dilute　oxygen　concentration　and　cool　pyrolysis　zone.　Moreover,　numerous　phosphorus-containing　species　acting　as　free　radical　scavengers　were　generated　during　degradation.　Silicon　dioxide　evolving　from　OapPOSS　protected　char　residues　from　thermal　degradation.　This　study　provides　a　novel　method　to　fabricate　high-performance　flame-retardant　EP　composites,　which　have　potential　applications　in　the　field　of　electrics　and　electronics.　Copyright　©　2017　John　Wiley　&　Sons,　Ltd.