The invention concerns a novel method for synthesis of 4-benzofuran-carboxylic acid or alkyl ester thereof. This method is characterized in that a reaction for aromatization of a compound of formula (II) is performed for the synthesis of the compound of formula (I), according to the scheme A2 below: ##STR00001## wherein R independently represents hydrogen or a linear or branched C.sub.1-.sub.15 alkyl group. With the invention, it is possible to industrially synthesize 4-benzofuran-carboxylic acid or alkyl ester thereof with good yield and very good purity.