A carboxylic ester is prepared by reacting a hydrocarbon selected from monoolefins having 2 to 6 carbon atoms, benzene, toluene and xylene with an aliphatic saturated carboxylic acid having 2 to 4 carbon atoms and molecular oxygen in the vapor phase in the presence of a supported solid catalyst of palladium metal, an antimony component and a carboxylic acid salt of alkali metal, alkaline earth metal, zinc, cadmium, lead or tin, with the improvement comprising: adding said antimony compound to the support of said catalyst by dipping a carrier into an aqueous solution of water-soluble antimony compound selected from the group consisting of antimonic acid, antimonates and antimony complexes of organic acids.