A series of (R)-3-amino-4-oxo-2, 3, 4, 5-tetrahydro-1, 5-benzothiazepine-5-acetic acids (4 and 13)and (S)-3-amino-4-oxo-2, 3, 4, 5-tetrahydro-1, 5-benzoxazepine-5-acetic acids (5 and 14) having an(S)-ω-amino-1-carboxyalkylamino group at the 3-position was prepared as part of our search for long-acting angiotensin converting enzyme (ACE) inhibitors. A number of derivatives had potent in vitro and in vivo ACE inhibitory activities. The structure-activity relationship of the series indicated that the duration of in vivo ACE inhibitory activity depends on the length of the carbon chain in the ω-aminoalkylamino substituent at the 3-position. The most prolonged activity was observed with (S)-8-amino-1-carboxyoctylamino derivatives (4d and 5d).