A method of producing an oxidation catalyst for cleaning exhaust gas, excellent in the function of oxidizing high boiling point materials such as particulates and polycyclic aromatic hydrocarbons contained in the exhaust gas of internal-combustion engines is provided. Metal elements A and B are selected so that the value of the ionic radius of metal element A/the ionic radius of metal element B is in the range of from 1.349 to 1.580. After reacting the grind mixed material of the first metal element A, the second metal element B, and urea, the reactant material is grind mixed, and thereafter subjected to firing at 600 to 1200° C. for 1 to 5 hours. By doing so, an oxidation catalyst for cleaning exhaust gas comprising a composite oxide represented by the general formula ABO3 is obtained.