The present invention herein provides a method for highly efficiently preparing high purity crystals of 2-amino-2-[2-[4-(3-benzyloxyphenylthio)-2-chlorophenyl]-ethyl]-1,3-propanediol hydrochloride. The method comprises the following steps: (1) dissolving 2-amino-2-[2-[4-(3-benzyloxyphenylthio)-2-chlorophenyl]ethyl]-1,3-propanediol in a mixed solvent comprising a solvent in which the compound in the form of the hydrochloride thereof is highly soluble and a solvent in which the compound in its hydrochloride is less soluble, to thus prepare a solution of 2-amino-2-[2-[4-(3-benzyloxyphenylthio)-2-chlorophenyl]ethyl]-1,3-propanediol； and then (2) adding hydrochloric acid to the resultant solution with stirring, to thus crystallize the hydrochloride of 2-amino-2-[2-[4-(3-benzyloxyphenylthio)-2-chlorophenyl]ethyl]-1,3-propanediol.本發明之課題在於提供有效率地製造2-胺基-2-[2-[4-(3-苄基氧基苯基硫化)-2-氯化苯基]乙基]-1,3-丙二醇鹽酸鹽之高純度結晶的方法。其解決手段係具有下列步驟。(1)將2-胺基-2-[2-[4-(3-苄基氧基苯基硫化)-2-氯化苯基]乙基]-1,3-丙二醇溶解於對於其鹽酸鹽之溶解度高之溶劑、與對於其鹽酸鹽之溶解度低之溶劑的混合溶劑，調製2-胺基-2-[2-[4-(3-苄基氧基苯基硫化)-2-氯化苯基]乙基]-1,3-丙二醇之溶液的步驟；其次(2)於前述溶液中，於攪拌下加入鹽酸，令2-胺基-2-[2-[4-(3-苄基氧基苯基硫化)-2-氯化苯基]乙基]-1,3-丙二醇之鹽酸鹽結晶化的步驟。
