Abstract: A method for producing an unsaturated carboxylic acid, which comprises subjecting an alkane to a vapor phase catalytic oxidation reaction in the presence of a catalyst containing a mixed metal oxide comprising, as essential components, Mo, V, Te, O and X wherein X is at least one element selected from the group consisting of niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony, bismuth, boron, indium and cerium, wherein the proportions of the respective essential components, based on the total amount of the essential components exclusive of oxygen, satisfy the following formulas:0.25<r.sub.Mo <0.980.003<r.sub.V <0.50.003<r.sub.Te <0.50.003<r.sub.X <0.5wherein r.sub.Mo, r.sub.V, r.sub.Te and r.sub.X are molar fractions of Mo, V, Te and X, respectively, based on the total amount of the essential components exclusive of oxygen.