The present invention relates to a production method of optically active 2-[(N-benzylprolyl)amino]-5-chlorobenzophenone (3) or a salt thereof, which includes reacting optically active N-benzylproline (1) with 2-amino-5-chlorobenzophenone (2) in acetonitrile and in the presence of an amide compound and thionyl chloride. According to the method of the present invention, optically active 2-[(N-benzylprolyl)amino]-5-chlorobenzophenone (3) or a salt thereof can be conveniently produced at a high purity and in a high yield: wherein * shows an asymmetric carbon atom and the configuration of the asymmetric carbon atom is S or R.