The　oxidation　behavior　of　B-bearing　high-speed　steel　was　studied　at　923K.　The　results　showed　that　the　as-cast　microstructure　of　1.0　wt.%B　high-speed　steel　was　composed　of　pearlite　+　ferrite　+　M-7(C,　B)(3)　+　M-2(B,　C).　When　the　boron　content　increased,　the　microstructure　gradually　changed　into　martensite　+　retained　austenite　+　netlike　M-2(B,　C)　+　M-23(C,　B)(6)　+　M-7(C,　B)(3).　The　cyclic　oxidation　of　B-bearing　high-speed　steel　at　K　followed　parabolic　rule.　The　unit　area　mass　gain　of　1　wt.%B　high-speed　steel　was　4.2　g/m(2)　after　923　K/250　h　oxidation,　and　the　unit　area　mass　gain　of　3　wt.%B　high-speed　steel　was　only　3.5　g/m(2).　The　oxidation　of　boron　element　formed　B2O3,　which　was　mainly　enriched　at　the　interface　of　the　oxide　film/matrix.　B2O3　flowed　in　the　oxide　film　at　high　temperature　and　was　easy　to　fill　the　defect.　B2O3　was　easy　to　form　B2O3-SiO2　borosilicate　with　SiO2.　The　more　boron　content　was,　the　more　favorable　it　was　to　form　B2O3-SiO2　borosilicate　oxide　layer　rich　in　B2O3　and　the　more　favorable　it　was　to　spread　in　the　oxide　film,　so　that　the　oxidation　resistance　of　B-bearing　high-speed　steel　could　be　remarkably　improved.