PURPOSE: To obtain in an industrially advantageous way the subject compound useful as an antibacterial agent, etc., by subjecting a diastereomer mixture of the 4-site ester of a specific 3-cephem-4-carboxylic acid derivative to an enzyme capable of asymmetrically hydrolyzing the mixture in an aqueous medium.

CONSTITUTION: This compound of formula II (* denotes an asymmetric carbon atom) useful as e.g. an antibacterial agent can be easily and efficiently obtained by subjecting a diastereomer mixture of the 4-site ester of a 3-cephem-4- carboxylic acid derivative of formula I [R1 is H or an acyl; R2 is a lower alkyl; R3 is a lower alkyl, a cycloalkyl, an aralkyl or a (substituted) phenyl; X is 0 or a single bond; Y is a group inert to the reaction] to an enzyme (or a material containing the same) capable of asymmetrically hydrolyzing said mixture in an aqueous medium.