NEW MATERIAL:A cis- or trans-1,5-benzothiazepine derivative expressed by formula I (R is CH3 or Cl).

EXAMPLE: trans-2, 3-Dihydro-3-hydroxymethyl-2-( 3-methylphenyl )-1, 5-benzothaze- pin-4(5H)-one.

USE: A medicine having inhibitory action on gastric acid secretion and antiulcer action, etc. with little side effects.

PROCESS: An ester derivative expressed by formula II is reduced in an inert solvent to give an alcohol derivative expressed by formula III, which is then reacted with methanesulfonyl chloride or p-toluenesulfonyl chloride in the presnce of a base to afford a sufonyloxy derivative expressed by formula IV (R' is CH3, etc.). The resultant sulfonyloxy derivative expressed by formula IV is then reacted with N-methylpiperazine to give the aimed compound expressed by formula I .