<p>Novel 7-methoxy-3-heterocyclic thiomethyl cephalosporin derivative possessing excellent antimicrobial activity represented by the general formula: wherein R1 represents group or HOOC- group, R2 represents a nitrogen-containing heterocylcic group, and M represents a hydrogen atom or a cation residue forming a salt and a process for producing 7-methoxycephalosporin antibiotic producing micro-organism belonging to the group Streptomyces by fermentation.</p>
