MoSi₂ alloys were prepared by mechanical alloying of Mo and Si powders. The microstructures of powders were characterized by XRD and SEM after different milling times. The formation procedures of MoSi₂ and phase transformations with temperature were investigated through the DSC and the RTA experiments. The powders milled for 6 hours showed the structure of fine mixture of Mo and Si. The tetragonal MoSi₂ phase and the hexagonal MoSi₂ phase appeared gradually in the powders milled for longer time. After 24 hours of milling, the average grain sizes of Mo and tetragonal MoSi₂ showed the nanocrystaliine structure. The DSC results showed exothermic peak at about 650℃ for the powders which were milled for 24 hours. The results showed that the unreacted fine mixture of Mo and Si transformed to the MoSi₂ phase by fast interfacial reaction which were in good agreement with the RTA results. The activation energy of this reaction was obtained from the Kissinger analysis and found to be 2.3 eV.