NEW MATERIAL:An epoxide derivative having an absolute configuration shown by the formula I (R1 is acyl; R2 is CH2OH, COOH, or alkoxycarbonyl) and its salt.

EXAMPLE: (2S, 3S)-2,3-Epoxy-3-(4-acetoxyphenyl)propanol.

USE: An intermediate for various kinds of optically active substances capable of producing diltiazem hydrochloride useful as Ca antagonists in high yield without carrying out optical resolution.

PREPARATION: A compound shown by the formula II (R3 is CHO, or COOH) is acylated to give a compound shown by the formula III, which is reduced to give a compound shown by the formula IV. This compound is selectively epoxidized to give a compound shown by the formula I a. If necessary, this compound is oxidized to give a compound shown by the formula I b, and, if necessary, it is esterified to give a compound shown by the formula I c.