In this study the effect of in situ Si3N4 formation in the microstructure of a Cordierite-Si3N4 composite using micro and nano silicon particles was investigated. It was found that micro and nano silicon particles have different reaction with the nitrogen in the matrix of cordierite at various temperatures. Result showed that using nano size silicon powder and increasing surface area formation of silicon nitride bonding will be increased which should be related to Si3N4 formation in low temperature and prevent to reacting with cordierite to form liquid phase during sintering. Additionally it was found that, it is possible to synthesis high porosity cordierite- Si3N4 composite with a good thermal shock resistance.