Highly　dense　AlN/BCN-nt　composites　with　1%-10%　(volume　fraction)　carbon-doped　boron　nitride　nanotubes　(BCN-nt)　were　fabricated　by　spark　plasma　sintering.　The　results　indicate　that　even　though　the　degradation　with　incorporation　of　BCN-nt　into　AlN,　the　thermal　conductivity　of　sintered　AlN/BCN-nt　composites　is　evidently　improved　with　the　growth　of　AlN　grains　and　the　elimination　of　oxide　contamination　by　increasing　sintering　temperature.　Both　the　real　part　and　imaginary　part　of　the　composites　of　Ka-Band　(26.5-40.0　GHz)　increase　with　the　increase　of　BCN-nt　content,　in　which　the　increase　of　imaginary　part　is　more　than　that　of　real　part,　resulting　in　an　increase　of　loss　factor.　Increasing　sintering　temperature　does　not　have　obvious　impact　on　the　dielectric　constant　value.　However,　excessively　high　sintering　temperature　(1700°C)　leads　to　damage　of　the　tubular　structure　of　BCN-nt　and　reduction　of　imaginary　part　of　the　composites.　The　AlN/BCN-nt　composites　with　appropriate　BCN-nt　content　and　sintering　temperature　possess　good　dielectric　dissipation　and　thermal　conductivity.