Highly pure (2R,3S)-3-tert-butoxycarbonylamino-1-chloro-2-hydroxy-4-phenylbutane or (2S,3R)-3-tert-butoxycarbonylamino-1-chloro-2-hydroxy-4-phenylbutane may be conveniently produced in high yield by: (a) reacting compound (1) with lithiumchloromethane to give compound (2) and at least a byproduct; (b) dissolving compound (2) and the byproduct in a polar solvent and adding water to the solution to precipitate compound (2) as crystals; (c) reducing the crystals of compound (2) to give compound (3) and at least its diastereomer as an impurity; (d) adding sulfuric acid thereto to give compound (4) and at least its diastereomer as an impurity; and (e) precipitating compound (4) as crystals from a solution containing acetic acid ester or acetic acid ester.