The phase relations in the Nd2O3-Y2O3 system were experimentally studied in the 1300 degrees-1600 degrees C range. X-ray diffraction, scanning electron microscopy, and electron probe microanalysis were applied to analyze the phase composition of annealed Nd2O3-Y2O3 mixtures with varying Y2O3 content. A thermodynamic assessment was conducted using the experimental data obtained. The excess Gibbs energies of the solution phases were described based on a simple substitutional solution model. A consistent set of optimized interaction parameters was derived for the Gibbs energy of the constituent phases, resulting in a good match between calculated and experimental data.