An oxidation catalyst for use in the oxidation of a substrate with a molecular oxygen, comprising at least one member selected from the group consisting of a specific hydrazyl radical (such as 2,2-diphenyl-1-picrylhydrazyl) and a specific hydrazine compound (such as 2,2-diphenyl-1-picrylhydrazine). A method for producing a chemical compound, comprising contacting a substrate with a molecular oxygen in the presence of the above-mentioned oxidation catalyst.