Abstract: Samples in the TiO2–CeO2 system with CeO2 concentrations ranging from 10 to 90 mol % were synthesized using the ceramic method. The phase composition of the obtained samples was determined by X-ray diffraction (XRD). Melting temperatures were measured by visual polythermal analysis. The composition and partial pressures of molecular vapor species over the TiO2–CeO2 system were determined across a wide range of condensed-phase compositions. For the melts in the studied system, component activities, Gibbs energies, and excess Gibbs energies were determined at 2150 K. It was shown that the system exhibits negative deviations from ideal behavior.