Vaporization processes and thermodynamic properties of samarium oxide over the temperature range 2265-2668 K have been studied by means of high-temperature mass spectrometry. The values of vaporization enthalpy of Sm(2)O(3)and enthalpy of formation of samarium monoxide at 298 K have been determined. Dependencies of partial pressures of SmO and Sm over Sm(2)O(3)as functions of temperature have been obtained over the above-mentioned range.