This paper focuses on the main factors on heat conductivity for carbon carbon composites: the orientation of the carbon fiber; the temperature of heat treatment and the microstructure of the pyrolytic carbon matrix. The results show that it is the CVD pyrolytic carbon that determines the heat conductivity of carbon carbon composites, and the effect of heat treatment temperature is limited. The results also show that the CVD pyrolytic carbon that has high concentration of RL has high heat conductivity.