The product formation of Mo-66.7at.%Si powders mixture during mechanical alloying using a high-energy vibratory type ball-milling machine was investigated by X-ray diffractometer (XRD). The temperature of the vial was measured at intervals during ball milling. The results showed that some MoSi2 was formed by the mechanically induced self-propagating reaction during a milling time of 105~110min; at the same time the surface temperature of the vial is increased. In early stages of milling, as a result of extensive fracturing and cold welding of powder particles, the interfacial energy between Mo and Si powders and cold deformation energy led to the formation of supersaturated solid solution of Mo(Si). And then mechanically induced self-propagating reaction of MoSi2 occurred immediately. After this, MoSi2 was gradually synthesized by diffusion. MoSi2 andMo(Si) were the end products, and the end products underwent the amorphous trend.