The present invention provides a method for purifying an amino acid contained in an aqueous solution of alkali metal salt of amino acid comprising the steps of: (1) cation exchanging, which comprises subjecting an aqueous solution of alkali metal salt of amino acid to a desalting purification treatment using a moving bed type continuous ion exchange apparatus comprising a cation exchange resin to obtain an aqueous solution of crude amino acid; and (2) anion exchanging, which comprises adsorbing to a weakly basic anion exchange resin an iminodicarboxylic acid, which is a coexisting by-product, in the resulting aqueous solution of crude amino acid to remove the iminodicarboxylic acid, wherein the aqueous solution of crude amino acid is passed even after adsorbing the iminodicarboxylic acid to the break through point of the weakly basic anion exchange resin.