The vapor composition and thermodynamic properties of components in the BaO-SiO₂ system at a temperature of 1970 K are determined using high-temperature mass spectrometry. The thermodynamic properties of melts in the BaO-SiO₂ system are calculated within the framework of the vacancy variant of the generalized lattice theory of associated solutions. This made it possible to establish the relation between the thermodynamic properties and the structural features of melts in the BaO-SiO₂ system.