The experimental and theoretical data on the structures and spectra of gaseous LaF and LaCl have been surveyed with the aim of selecting molecular constants for the states with excitation energies in the range 0–10 000 cm⁻¹. With the use of these data, the thermodynamic functions in the range 298.15–3000 K have been calculated from statistical sums in which the intramolecular component was found by direct summation over the energy levels and in the rigid rotator-harmonic oscillator approximation with additional inclusion of the anharmonicity of oscillations (by the method of Mayer and Goeppert-Mayer) and correction for centrifugal stretching. In the latter case, the contribution made by electronic excitation has been calculated by two methods: based on the energies of the excited states of molecules and based on the electronic excitation energy of the free La⁺ ion. The adequacy of the description of the thermodynamic functions is demonstrated by the calculations of the enthalpies of atomization of LaF and LaCl from experimental data obtained when studying high-temperature reactions with the participation of these halides.