PURPOSE: To provide a process capable of producing 2,4-dihydroxybenzaldehyde in high yield in an easily purifiable state and producing 2-hydroxy-4- methoxybenzaldehyde in high selectivity and yield.

CONSTITUTION: This invention relates to a process for producing 2,4- dihydroxybenzaldehyde from 1,3-dihydroxybenzene and dimethylformamide by adding a halogenated hydrocarbon in the presence of phosphorus oxychloride and to a process for producing 2-hydroxy-4-methoxybenzaldehyde from 2,4- dihydroxybenzaldehyde and dimethyl sulfate in a mixed solvent consisting of an essentially water-immiscible organic solvent and an aqueous solution of an alkali metal carbonate.