An aromatic dicarboxylic acid of chemical formula HOOC—Ar1—COOH is prepared in a process wherein a feedstock comprising at least an aromatic aldehyde compound of chemical formula (1): OHC—Ar1—COOH, wherein Ar1 represents an arylene or heteroarylene moiety, and an aqueous electrolyte are provided; the feedstock and the aqueous electrolyte are introduced into an electrolytic cell comprising electrodes, wherein at least one of the electrodes comprises a non-noble metal and/or an oxide and/or a hydroxide thereof and/or carbon; and the aromatic aldehyde compound of formula (1) is oxidized electrochemically to yield the aromatic dicarboxylic acid.