An antibacterial 7-protected amino-3-oxyiminomethyl-3-cephem-4-carboxylic acid is prepared by the reaction of a 7-protected amino-3-formyl-3-cephem-4-carboxylic acid or its reactive derivatives with a hydroxylamine compound or its reactive derivatives, the process being more suitable for large scale production when coupled with fermentative production of a 3-hydroxymethyl-3-cephem-4-carboxylic acid followed by its direct oxidation.