SiB0.5C1.5N0.5　nanopowders　were　synthesized　by　mechanical　alloying　method,　and　a　predominantly　amorphous　with　a　small　volume　fraction　of　nanocrystalline　phase　was　formed　in　the　powders.　The　results　showed　that　the　crystallites　were　SiC,　and　the　polytype　of　SiC　were　3C　and　6H.　SiB0.5C1.5N0.5　powders　were　consolidated　by　spark　plasma　sintering　(SPS)　technique　at　1800　degrees　C　under　different　sintering　pressure.　The　grain　boundaries　of　SiC　and　BCN　phase　could　not　be　clearly　distinguished　for　the　ceramics　sintered　under　25　MPa.　When　the　pressure　increased　to　40MPa,　SiC　phase　almost　completely　crystallized,　and　its　grain　size　was　less　than　1　mu　m.　BCN　phase　were　mainly　distributed　at　boundary　of　SiC　grain.　Some　amorphous　structures　were　found　in　the　sintered　ceramics.　Relative　densities　of　the　ceramics　increased　from　76.6%　to　92.4%,　and　mechanical　property　values　increased　two　or　three　times　with　the　increase　of　sintering　pressure.　For　the　ceramics　sintered　under　a　pressure　of　40　MPa,　flexural　strength,　fracture　toughness,　elastic　modulus　and　Vickers＇　hardness　attained　to　311.5　MPa,　3.45　MPa　m(1/2),　133.0　GPa　and　3.68　GPa,　respectively.　The　mass　of　the　SiBCN　ceramics　lose　by　several　percent　below　930　degrees　C　in　air,　and　then　keep　unchanged　above　1100　degrees　C.　(C)　2007　Elsevier　B.V.　All　rights　reserved.