This study reports the use of X-ray diffraction quantitative phase analyses in NiTi alloys produced by MARES (Mechanically Activated Reactive Extrusion Synthesis). These analyses were performed with the PowderCell 2.4 software. The mechanically activated powders heated in a DTA furnace at 500 °C had as main phases Ni (27 wt %) and Ti (30 wt %) and the major intermetallic phase was Ni3Ti (20 wt %). Above 500 °C the intermetallic phases were predominant. At 600 °C the major phase was Ni3Ti (29 wt %) and at 700 °C was NiTi2 (32 wt %). In this temperature range the NiTi was a minor intermetallic phase (14-20 wt %). No changes in the constitution or in the amount of the phases were detected between the degassed powder samples and the extruded materials. The intermetallic phases were always predominant and the major was Ni3Ti (27-32 wt %). The NiTi phase content was in a range of 15-22 wt %. The weighted residual error, Rwp, of the fittings ranged between 17 and 27. Using the Williamson and Hall plot, crystallite sizes within the range of 26-53 nm and of 12-25 nm were evaluated for the metallic and intermetallic phases, respectively. Vickers micro-hardness measurements were virtually unchanged with the extrusion parameters but increased relatively to the mechanically activated powders.