For the melts of the system SrO-B₂O₃-SiO₂ the processes of vaporization were studied by the method of high-temperature mass-spectrometry and the values of activities of components and their Gibbs energies of formation, and also corresponding excess functions were determined. Negative deviations from ideal behavior are observed in the melts of the studied system at 1720 and 1800 K.