According to the present invention which comprises subjecting an aqueous solution of 2-keto-L-gulonic acid or its water-soluble salt containing an acid impurity, whose acidity is higher than that of 2-keto-L-gulonic acid, to contact with an anion-exchange resln, then allowing the 2-keto-L-gulonic acid or the water-soluble salt thereof to precipitate from the processed solution obtained by allowing the impurity to be absorbed, 2KGA or its water-soluble salt of a high purity can be separated in a high yield from an aqueous solution of 2KGA or its water-soluble salt containing acid impurities with less number of steps a compared with conventional methods.
