A 5-(3-cyanophenyl)-3-formylbenzoic acid compound of the formula (IV) is prepared by reacting a 5-bromo-3-(hydroxymethyl)benzoic acid compound of the formula (I) with manganese dioxide to provide a 5-bromo-3-formylbenzoic acid compound of the formula (II), and then reacting the resultant compound of the formula (II) with 3-cyanophenylboronic acid of the formula (III) in the presence of a palladium complex. ##STR1##

R is a H atom or a C₁-C₁₀ alkyl group.