Boron　carbide　ceramic　has　been　known　to　possess　ultrahigh　hardness　and　good　thermal　conductivity.　However,　these　properties　greatly　depend　on　the　phase　composition　of　boron　carbide,　that　is,　the　B/C　ratio.　As　the　combined　B/C　ratio　in　boron　carbide　deviates　from　the　stoichiometry　of　B4C,　all　these　properties　decrease　dramatically.　In　this　study,　the　phase　compositions　of　several　commercial　boron　cabide　powders　were　confirmed　through　the　detailed　analysis　of　their　X-ray　diffraction　patterns,　from　which　the　diffraction　peaks　of　the　boron-rich　phases　were　separated　and　calibrated　from　the　overlapping　peaks.　The　final　phase　compositions　of　hot　pressed　boron　carbide　ceramics　and　the　transformation　process　of　boron-rich　phases　to　B4C　at　different　sintering　temperatures　were　then　investigated.　The　results　show　that　the　commercial　boron　carbide　powder　is　usually　a　mixture　of　B4C　and　boron-rich　phases　such　as　B6.5C　as　well　as　other　impurities.　The　results　of　X-ray　diffraction　and　Raman　spectroscopy　show　that　the　boron-rich　phases　react　with　free　carbon　to　form　B4C　as　the　sintering　temperature　increases.　A　boron　carbide　ceramic　with　pure　B4C　phase　is　prepared　using　commercial　boron　carbide　powder　by　hot　pressing　at　2100　degrees　C　and　40　MPa　for　60　min.