The ternary phase diagram Ni–Sn–Ti has been assessed by a general Calphad procedure. Ab-initio calculations using the VASP code have been made to obtain the enthalpies of formation of the compounds and the enthalpies of mixing along two key sections. Phase modeling provides a complete description of the system. Three phases exist in this system: NiTiSn, Ni2TiSn and Ni2Ti2Sn. Moreover the NiTi5Sn3 phase resulting from the filling with Ni of the 2b Wyckoff sites in the Ti5Sn3 binary phase has been considered as an ordered structure. Isotherm sections are shown in order to understand the stabilities of phases and some isopleth sections are drawn together with the experimental data of liquidus arrests.