A process for the industrial production of 2-amino-2-[2-[4-(3-benzyloxyphenylthio)-2-chlorophenyl]ethyl]-1,3-propanediol hydrochloride (Compound I), an effective immunosuppressant. The process for producing 2-amino-2-[2-[4-(3-benzyloxyphenylthio)-2-chlorophenyl]ethyl]-1,3-propanediol hydrochloride or a hydrate thereof includes the steps of reacting 4-(3-benzyloxyphenylthio)-2-chlorobenzaldehyde with ethyl diethylphosphonoacetate in a solvent in the presence of a base to form ethyl 3-[4-(3-benzyloxyphenylthio)-2-chlorophenyl]acrylate； reducing the resulting ethyl 3-[4-(3-benzyloxyphenylthio)-2-chlorophenyl]acrylate, followed by mesylation, iodination and nitration, to form 1-benzyloxy-3-[3-chloro-4-(3-nitropropyl)phenylthio]benzene； forming 2-[2-[4-(3-benzyloxyphenylthio)-2-chlorophenyl]ethyl]-2-nitro-1,3-propanediol using a formaldehyde solution； and reducing the resulting 2-[2-[4-(3-benzyloxyphenylthio)-2-chlorophenyl]ethyl]-2-nitro-1,3-propanediol to form the desired product.
