PURPOSE: To inactivate an esterase enzyme coexisting with D-amino acid oxidase in production of glutaryl-7-aminocephalosporanic acid by using D-hmino acid oxidase-containing substance derived from a microorganism capable of producing D-amino acid oxidase from cephalosporin C.

CONSTITUTION: In production of glutaryl-7-aminocephalosporanic acid by using D-amino acid oxidase-containing substance derived from a microorganism capable of producing D-amino acid oxidase from cephalosporin C. The microorganism capable of producing D-amino acid oxidase is treated by UV rays, X-ray irradiation or with a modifying agent to reduce esterase producing ability ≤5% of D-amino acid oxidase producing ability is used.