Al substituted MoSi2 composites were prepared by using microwave assisted synthesis method, which is a self-propagation synthesis ignited by microwave energy. The composition and microstructure of as combusted powder had been detected by XRD and SEM analysis. Result shows that the pre-heating temperature and phase composition of microwave assisted combustion synthesis is largely influenced by the content of aluminum. The phase structure of Mo(Si, Al)2 alter from a mixture of MoSi2 and Mo5Si3 to nearly pure Mo (Si, Al)2 with the increasing of Al substitution. The main mechanism is dissolution separation..