The solubility of 1,6-naphthalene disulfonic acid disodium in binary sodium chloride + water, sodium sulfate + water, and ethanol + water solvent mixtures was measured in temperature range from (273.15 to 323.15) K by a steady-state method. Results of these measurements were correlated by a modified Apelblat equation. It was found that sodium chloride + water is the best solvent mixture for purifying 1,6-naphthalene disulfonic acid disodium.