Nanocrystalline Cu50Mg30Ni20 and Cu50Mg45Ni5 alloys were synthesized by mechanical alloying from mixtures of pure crystalline Cu, Mg and Ni powders using a Fritsch planetary ball mill with certain weight ratio of ball to powder. Structural evolution and thermal properties of these alloys were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray diffraction patterns were examined with the help of Fullprof program by employing Rietveld refinement technique. According to the present results, the crystallite size of Cu-Mg-Ni powders decreased with increasing milling time. Average crystallite size was calculated by three methods; Rietveld refinement technique, Debye Scherrer equation, TEM observation and, it was determined in the range of 10-20 nm. After 25 h of milling nanostructured three phases such as Cu-based solid solution (Cbs), Mg-0 Ni-85(0.15) and MgO were obtained. The lattice parameter of the Cbs phase varied from 3.61 to 3.66 A during different stages of milling from 5 to 25 h. DSC traces of the mechanically alloyed Cu-Mg-Ni powders showed two exothermic peaks after being milled for 10-15 h. (C) 2013 Elsevier B.V. All rights reserved.