Abstract: Process for stereoselectivity preparing a cis-form of 5-(aminoalkylamino)-1,5-benzothiazepine derivative represented by formula (VI): ##STR1## is provided, said process comprising carrying out a stereoselective addition reaction of an o-(aminoalkylamino) thiophenyl derivative with a trans-substituted glycidic ester at an elevated temperature in a nonpolar solvent in the presence of a divalent or trivalent iron ion to prepare a threo-form intermediate, hydrolyzing the ester group of said intermediate, acetylating the hydroxyl group of said hydrolyzed compound, and subjecting said acetylated compound to a ring closure reaction to obtain the objective compound (VI).