Two new 3-cyano-3-cephem derivatives, potassium 3-cyano-3-cephem-4-carboxylate (2) and potassium 7α-phenylacetamido-3-cyano-3-cephem-4-carboxylate (3), were prepared from 7β-aminocephalosporanic acid. Compounds 2 and 3 showed only weak β-lactamase inhibitory activity in contrast to sodium 7α-[(1R)-1-hydroxyethyl]-3-cyano-3-cephem-4-carboxylate (1), indicating the important role of the 7α-(1-hydroxyethyl) substituent for β-lactamase inhibitory activity.