Thin films of magnesia have been deposited by a novel spray pyrolysis method. An aqueous magnesium acetylacetonate solution was ultrasonically nebulized, transported in flowing oxygen, and thermally decomposed on silicon (100), sapphire, and fused silica at temperatures between 400 and 550 °C. The films were from 0.1 to 0.5 &mgr;m thick, optically transparent, and smooth. The MgO films were poorly crystalline as deposited. MgO films on sapphire crystallized with strong (100) orientation after annealing at 700 and 930 °C in flowing oxygen.