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 Delta H (by DSC) peak in the range of estimated enthalpy even after 24 h milling. The similarity of the mechanism of structural development by mechanical alloying of the Ni76Si24 powder mixture, and by mechanical milling of Ni76Si24 compound was also investigated in this study.