Using the Rietveld refinement, we analysed the structural evolution of Ni 50 Ti 50 alloy prepared by mechanical alloying method. The elemental Ti and Ni powders are milled during different milling times (0, 1, 3, 6, 24, and 72 hours) in a high-energy planetary ball mill (Pulverisette 7 premium line). The milled powder specimens were characterized with x-ray Philips X,Pert diffractometer equipped with CuK radiation source ( Cu 0.15418 nm). We refined the structure of compounds using the MAUD program, and we found structural parameters such as the atomic positions (x, y, z), symmetry, and a space group. Moreover, microstructural parameters such as the lattice parameters (a, b, c), the average crystallite size , microstrains 2 1/2 , the average number of compacted layers, and the phase percentages were also determined. According to the results, at the initial stages of milling (typically of 1-3 h), the structure consists of Ni-based solid solution [f.c.c.-Ni (Ti)],