Three-dimensional　boron　nitride/zinc　oxide　(3D-BN-ZnO)　scaffolds　were　prepared　by　the　ice-templating　method,　in　which　ZnO　particles　were　in　situ　formed　by　sintering.　Then,　polydimethylsiloxane　(PDMS)/3D-BN-ZnO　composites　were　fabricated　via　vacuum　infiltration　of　PDMS　prepolymer　into　the　scaffolds　and　curing.　Compared　with　the　composite　prepared　by　simple　blending,　the　thermal　conductivity　of　the　composite　prepared　based　on　the　ice-templating　method　is　much　higher　due　to　the　excellent　orientation　of　hexagonal　boron　nitride　(hBN)　sheets.　Based　on　the　same　content　of　hBN　sheets,　the　further　introduction　of　2.7 wt%　ZnO　particles　formed　in　situ　by　sintering　could　promote　the　thermal　conductivity　of　the　composite　to　the　value　of　1.45　W　m−1 K−1,　which　is　70.6%　higher　than　that　of　the　PDMS/3D-BN　composite.　In　addition,　compared　with　the　PDMS/3D-BN　composite　containing　more　hBN　sheets,　the　PDMS/3D-BN-ZnO　composite　with　2.7 wt%　ZnO　particles　possesses　fewer　fillers　but　higher　thermal　conductivity.　It　suggests　that　ZnO　particles　could　synergistically　improve　the　thermal　conductivity.　As　revealed　from　the　morphology　of　the　composites,　many　ZnO　particles　are　located　between　hBN　sheets　and　thus　construct　thermally　conductive　paths.　This　study　provides　a　new　strategy　for　the　design　of　thermal　interface　materials　with　high　thermal　conductivity.　©　2022　Society　of　Plastics　Engineers.