Thermal stress is one of the main reasons leading to the boron carbide pin rupture when used in nuclear reactors. The higher the thermal conductivity and the lower the thermal expansion coefficient, the greater the thermal stress is . So, a correct and reliable evaluation of these properties is a guarantee to the safe application of the materials. The thermal conductivity was measured by laser flash method and the thermal expansion coefficient was determined by DF1500 dilatometer. The relationship between thermal conductivity and the temperature, porosity or grain size were studied. A comparison of the present results to the literature data was also dealt with. It was gained that the thermal conductivities are in accord with the results from the literatures when the temperature is above 300 ℃; while a little lower than that from literatures, when the temperature was below 300 ℃. It is caused maybe by the poor contact of the thermocouple to the sample surface, as the poor thermal conductivity of boron carbide at lower temperature and no goldcoating on it. The relationship between thermal conductivities and porosities can be described as 1/λ=2+0.005 5t or 1/λ=(6.28t+1 840)×105. The influence of grain sizes on the thermal conductivities can be described as λ=λs(1-θ)(2+2.2θ) or λ=λs(1-1.5θ). The thermal expansion coefficients are fully in agreement with the literature data.