A method of decolorizing a colored effluent comprising (i) a colored substance; and (ii) a polyvalent carboxylic acid or a polyvalent aminocarboxylic acid, the method including the steps of: (a) controlling a hydrogen ion exponent (pH) of the colored effluent to be in a range in which two or more carboxylic acid groups in the polyvalent carboxylic acid or the polyvalent aminocarboxylic acid does not dissociate; (b) adding an inorganic metal salt to the colored effluent so as to allow the inorganic metal salt to react with the colored substance to form a precipitation in the colored effluent, and (c) eliminating the precipitation from the colored effluent.