Mechanical alloying is a non-equilibrium process for materials synthesis. It has been used to obtain nanocrystalline binary system FeNi. Fe and Ni elemental powders have been ball milled in a planetary mill (Pulverisette 7, Fritsch) for various times up to several hours. The morphology of the powders was examined using scanning electron microscopy (SEM). X-ray diffraction (XRD) has been employed to follow the structural evolution during the ball milling process. The X-ray patterns were analysed by the MAUD procedure, which is based on the Rietveld method combined with a Fourier analysis, well adapted for broadened diffraction peaks. The grain size was found to be about 5 nm and the residual strain was about 0.021 % after 322 h of milling. The as-milled samples, characterized by Mossbauer spectroscopy (MS) contain a mixture of alpha (bcc) and gamma (fcc) phases after 48 h of ball milling. (c) 2005 Elsevier B.V. All rights reserved.