B4C and SiC particle-dispersed carbon composite were fabricated from calcined pitch coke, B4C and SiC with various particle size by grinding and then pressureless sintering. During non-isothermal oxidation test up to 1400°C in air atmosphere, oxidation behavior of the C/B4C/SiC composite was clarified by means of calculation of kinetic parameters using experimental data of mass change, gas formation of CO2, and oxygen gas consumption. Amount of the matrix carbon oxidized above 800°C in the composite with SiC particle of 0.4 µm and 0.9 µm in size was less than that in the composite with SiC particle of 50 nm and 1.8 µm in size. The oxidation of the matrix carbon was shown to depend upon the formation of B2O3 glass below 800°C oxidation, and that of SiO2 glass above 800°C. The composite containing SiC with 20 nm in size was stable against oxidation above 1400°C except the temperature ranging from 900°C to 1100°C.