A method of producing an α,β-unsaturated dicarboxylic acid ester exemplified by an α-hydromuconic acid ester from a carboxylic acid ester exemplified by a 3-hydroxyadipic acid ester or a 3-hydroxyadipic acid-3,6-lactone ester, in which the selectivity for the α,β-unsaturated dicarboxylic acid ester can be increased by subjecting the carboxylic acid ester to a basic condition of pH 8.5 to less than 13 in an organic solvent or a mixed solvent of an organic solvent and water.