Abstract: The present invention relates to novel cephalosporin derivatives, processes for preparing thereof, compositions for preventing and/or treating infectious diseases which comprise the novel cephalosporin derivatives as active components, and the intermediate compounds in the synthesis of cephalosporin derivatives and processes for producing thereof.The present invention is based on the selection of groups containing a condensed heterocyclic ring, particularly a triazolopyrimidine ring or a thiadiazolopyrimidine ring, as substituents at the 3-position of the cephem skeleton, and of groups containing a catechol moiety, particularly a catechol carboxymethyloxyimino moiety or a catechol carboxyimino moiety, as substituents at the 7-position of the cephem skeleton.The compounds of the present invention containing the aforementioned substituents have a strong antibacterial activity against Gram-negative bacteria and also against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus.