The ternary systems La2O3-SrO-Ga2O3, La2O3-MgO-Ga2O3, and SrO-MgO-Ga2O3 were studied at 1400 degreesC in air, with emphasis on LaGaO3, The compound exhibited a small solid solubility of strontium substituting for lanthanum and also of magnesium substituting for gallium, In the system La2O3SrO-Ga2O3, LaGaO3 existed only within a very narrow concentration region, whereas in the system La2O3-MgO-Ga2O3, LaGaO3 was in equilibrium with most of the phases of the system. The system SrO-MgO-Ga2O3 at 1400 degreesC in air was characterized by an extended liquid phase at similar to 1185 degreesC.