Abstract: A new method for production of a cephalosporin ester (I) which comprises reacting a derivative of an organic acid (II) with a 7-aminocephem compound (III) in the presence of an enzyme of a microorganism of one of the genera Escherichia, Bacillus, Proteus and Pseudomonas: ##SPC1## ##EQU1## ##SPC2## wherein R is an unsaturated six-membered carbocyclic ring or five-membered heterocyclic ring residue which may optionally have uncharged substituent groups; R.sup.1 is hydrogen or an uncharged substituent group such as hydroxyl or halogen; R.sup.2 is a hydrogen atom or an organic group which is bound through an oxygen, sulfur or nitrogen atom; COOR.sup.3 is a group which may easily be converted to COOH.