PURPOSE: To efficiently obtain a 3-hydroxymethylcephalosporanic acid derivative useful as an intermediate, etc., for cephalosporin-based antibiotic substances in high yield under mild conditions by reacting a specific cephalosporanic acid lactone derivative with a hydrolase, etc., derived from a microorganism.

CONSTITUTION: A cephalosporanic acid lactone derivative of formula I [R is R1-CO; R1 is (substituted)phenyl, amino, carboxyl, (substituted)phenyl-substituted 1-8C alkyl] is made to react with one or two or more selected from a hydrolase derived from a microorganism, a hydrolase derived from an animal (e.g. a lipase) and a prepared substance thereof to afford the objective derivative of formula II.