Provided is a method of oxidizing a substrate with excellent oxidizing power to yield a corresponding oxide. The method can employ a commercially available imide compound as intact as a catalyst and can produce the oxide in a high yield under mild conditions.A method for producing an oxide according to the present invention includes performing oxidation of a substrate in the presence of oxygen and ozone under catalysis of an imide compound to yield a corresponding oxide. The imide compound has a cyclic imide skeleton represented by Formula (I). In the formula, n is selected from 0 and 1; and X is selected from an oxygen atom and an —OR group, where R is selected from hydrogen and a hydroxy-protecting group.