PURPOSE: To industrially advantageously obtain the title compound useful as an intermediate for antiphlogistic, analgesic and antipyretic agents in one stage and easy reaction operation by reacting substituted benzenes with pyruvic acid in the presence of Lewis acid in a solvent and then hydrolyzing the resultant product.

CONSTITUTION: For example, substituted benzenes expressed by formula I or formula II (X and Y are 1-5C straight-chain or branched alkyl and further X is halogen) are reacted with pyruvic acid of 0.3-4 times by mol, preferably 0.5-2.5 times by mol based on the above-mentioned compound in the presence of a Lewis acid, preferably inorganic acid, especially inorganic aluminum chloride of 0.1-7 times by mol, preferably 0. 5-3 times by mol based on the above- mentioned compound in a solvent (preferably methylene chloride), normally at - 60 to +60°C, preferably at -40to +30°C and then hydrolyzed to industrially advantageously provide the title compound useful as a precursor for 2-(4- substituted phenyl)propionic acid (the above-mentioned medicine).