The purpose of the present study was to examine the thermodynamic properties and vaporization processes in the Sm₂O₃–ZrO₂ system by the Knudsen effusion mass spectrometric method (KEMS). The samples in the system under consideration were synthesized by the solid-state method using a high-energy ball mill. Vapor over the Sm₂O₃–ZrO₂ system consisted of SmO, Sm, and O in the temperature range 2200–2540 K. Concentration dependences of the SmO and Sm partial vapor pressures, the component activities, and excess Gibbs energies were obtained at a temperature of 2452 K in the compositional range of 0.23–0.73 Sm₂O₃ mole fraction. These data evidenced negative deviations from the ideal behavior and a possibility to use the subregular solution model to describe the concentration dependences of the thermodynamic properties in the Sm₂O₃–ZrO₂ system. Correlations were found between the observed changes in the thermodynamic behavior of the system mentioned and the relative number of bonds when the second coordination sphere was taken into consideration in the condensed phase calculated by the Generalized Lattice Theory of Associated Solutions.