Aluminum　nitride/boron　nitride　(AlN/BN)　ceramics　with　15-30　vol.%　BN　as　secondary　phase　were　fabricated　by　spark　plasma　sintering　(SPS),　using　Yttrium　oxide　(Y2O3)　as　sintering　aid.　Effects　Of　Y2O3　content　and　the　SPS　temperature　on　the　density,　phase　composition,　microstructure　and　thermal　conductivity　of　the　ceramics　were　investigated.　The　results　revealed　that　with　increasing　the　amount　of　starting　Y2O3　in　A/N/BN,　Yttrium-contained　compounds　were　significantly　removed　after　SPS　process,　which　caused　decreasing　of　the　residual　grain　boundary　phase　in　the　sintered　samples.　As　a　result,　thermal　conductivity　of　AlN/BN　ceramics　was　remarkably　improved.　By　addition　Of　Y2O3　content　from　3　wt.%　to　8　wt.%　into　AlN/15　vol.%　BN　ceramics,　the　thermal　conductivity　increased　from　110　W/m　K　to　141　W/m　K.　Crown　Copyright　(C)　2009　Published　by　Elsevier　Ltd　and　Techna　Group　S.r.l.　All　rights　reserved.