To obtain a method for producing an unsaturated carboxylic acid from an olefin by a one-stage reaction in a high yield.

In this method for producing an unsaturated carboxylic acid by subjecting an olefin to a vapor-phase catalytic oxidation reaction in the presence of a compound oxide catalyst, the method for producing an unsaturated carboxylic acid is characterized by using the compound oxide catalyst comprising at least molybdenum(Mo), vanadium(V) and antimony(Sb) as essential components.