Experimental samples were produced with mullite and cordierite powders with SiC. Effects of temperature, atmosphere and additive on the composite properties were investigated by XRD, STA and PSA methods. Results show that samples containing calcinate cordierite and calcinate mullite with SiC baked in air atmosphere have not suitable properties at the temperature range of due to SiC intensive oxidation, while argon atmosphere decrease SiC oxidation. Using as the additive, cordierite phase formation and prevention from SiC oxidation at low temperatures were achieved, leading to the improvement of physical and mechanical properties