PURPOSE: To provide production of the subject compound having extremely improved yield only of a target substance by approximately the same operation as that of the conventional method.

CONSTITUTION: In reacting 2-amino-8-hydroxynaphthalene-6-sulfonic acid with 2,6-dimethylaniline in the presence of a sulfite, the reaction is carried out in the presence of sodium hydrogensulfate or sulfuric acid to give 2-(2',6'- dimethylphenyl)amino-8-hydroxynaphthalene-6-sulfonic acid. In the case of using sodium hydrogensulfite as the sulfite and sodium hydrogensulfate, the amount of sodium hydrogensul fate added is 0.02-0.3mol, preferably 0.1-0.2mol based on 1mol of sodium hydrogensulfite. The initial pH of the reaction system in the reaction is 3.3-3.9 in the case of the added amount of the former and is 3.3-3.6 in the case of the added amount of the latter.