The effect of high energy milling on powders of a FeNi (50/50) alloy and a 316L stainless steel has been evaluated by means of X-Ray Diffraction (XRD). The average microstrain as function of the milling time (1/2h, 1h and 8h) was determined from XRD data. The displacement and broadening of the (XRD) peaks were used for estimate the stacking fault energy (SFE), using the method of Reed and Schramm. It was estimated SFE=79 mJ/m2 for the FeNi (50/50) alloy and SFE=14 mJ/m2 for the 316L stainless steel. The better experimental conditions for determining the SFE by XRD are discussed.