A systematic thermodynamic description for the Mg-rich corner of La-Mg-Ni ternary system has been obtained using the CALPHAD approach. The substitutional solution model, the three-sublattice model and the stoichiometric compound model were used to describe the liquid, La2Mg17-xNix and LaMg2Ni phases, respectively. The model parameters were then optimized using the experimental information. Calculations were compared with the experimental data for the enthalpy of mixing in liquid, isothermal sections at 673 and 773 K, invariant reactions and partial liquidus surface. The calculation and the experimental data are in good agreement.