Gaseous CePO ₂ has been identified by Knudsen effusion mass spectrometry during vaporization of CeO ₂ and magnesium diphosphate from tungsten double, two-temperature effusion cell. Structure and molecular parameters of gaseous cerium phosphate under study were determined using quantum chemical calculations. On the basis of equilibrium constants measured for gas-phase reaction, standard formation enthalpy of CePO ₂ was determined to be −508 ± 41 kJ ⋅ mol ⁻¹ at the temperature 298 K.