Abstract: A method for producing naphthalenedicarboxylic acid comprising the steps of: dissolving 2,6-dimethylnaphthalene in acetic acid solvent; oxidizing the product from the dissolution process using oxygen and a diluent gas; crystallizing naphthalenedicarboxylic acid that has been produced from the oxidation process; and separating the crystallized naphthalenedicarboxylic acid, wherein the amount of the diluent gas being discharged from and recycled to the oxidation process is controlled during the oxidation process, and the amount of mother liquor being recycled to the dissolution process after crystallization is controlled during the separation process, is provided.