Nickel and silicon powders, of average composition Ni3Si, were mechanical alloyed in a high energy ball mill. The severe plastic deformation produced by mechanical milling induced transformations with increasing milling time as follows: mixture of elemental Ni and Si powder → f.c.c. solid solution → nanocrystalline f.c.c. The structural evolution with milling time was followed by X-ray diffraction, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). Complete f.c.c. solid solution occurred at a milling time of 4 h and the saturated ΔH (by DSC) peak in the range of estimated enthalpy even after 24h milling. The similarity of the mechanism of structural development by mechanical alloying of the Ni76Si24 powder mixture, and by mechanical milling of Ni7 6Si24 compound was also investigated in this study.