Abstract: FeSiAl nanocrystalline alloy powders were prepared by mechanical milling in inert atmosphere of argon at room temperature.The effects of alloying process on grain size and micro strain of the alloy powders were investigated by XRD.The micro images and solid phase transformation of the nanocrystalline powders were studied by SEM and DSC.The results show that Al and Si atoms have intermingled with the crystal lattice of Fe and formed solid solution during the cold welding.With the increase of the milling time the grain sizes of the alloy powders decrease sharply and the micro strain increases and the average grain size is about 9 nm after milling for 40 hours.The nanocrystalline alloy powders are in the unstable situation and have low phase transition temperature because of the great distortion of lattice and micro strain formed during the milling.