Experimental data on solubility of magnesium oxide in melts based on mixed chlorides of alkali and alkaline earth metal are complemented by investigation in SrCl2-rich melt of KSr2Cl5 composition. The changes of MgO solubility in the chloride melts based on CaCl2 and SrCl2 at melt temperature variation obeys to predictions of the Shreder-Le Chatelier equation. This brings MgO solubility in the different melts to the same conditions (T=973 K). The oxoacidic properties of the melt strengthen with increase of the concentration of alkaline earth cations and different complexes are formed due to the solvation of oxide ion in the melts based on these cations: BaO in Ba2+-based chloride melts and 2SrCl(2).SrO in Sr2+-based ones. In CaCl2-based melts simultaneous formation of complexes of 4CaCl(2).CaO and 2CaCl(2).CaO compositions is possible. (C) 2017 Elsevier Ltd.