To provide a method for purifying 6,6'-(ethylenedioxy)bis-2-naththoic acid, by which the highly pure 6,6'-(ethylenedioxy)bis-2-naththoic acid little in the contents of alkali metals can be obtained.

This method for purifying the 6,6'-(ethylenedioxy)bis-2-naththoic acid comprises holding the crude crystals of the 6,6'-(ethylenedioxy)bis-2-naththoic acid containing 10 to 1,000 mass ppm of potassium and/or sodium in the presence of an aliphatic carboxylic acid in one or more aprotic polar organic solvents selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone and dimethylsulfoxide at 0 to 300C.