7-Carboxymethoxyphenylacetamido-3-cephem derivatives represented by the formula ##STR1## wherein R.sub.1 means hydroxy, C.sub.1 -C.sub.4 alkanoyloxy or C.sub.1 -C.sub.4 alkoxycarbonyloxy, R.sub.2 is hydrogen or methoxy, R.sub.3 denotes C.sub.1 -C.sub.4 alkanoyloxy, substituted or unsubstituted nitrogen-containing heterocyclic-thio or substituted or unsubstituted pyridinium with a proviso that, when R.sub.3 denotes the substituted or unsubstituted pyridinium, R.sub.3 forms an intramolecular salt with the carboxy at the 4-position of the cephem nucleus, and A is a group of the following formula: ##STR2## in which R.sub.4 and R.sub.5 are individually hydrogen or C.sub.1 -C.sub.4 alkyl, and their pharmaceutically acceptable salts, exhibit excellent anti-bacterial activities against Gram-negative bacteria, particularly, Pseud. aeruginosa, Kleb. pneumoniae, Ser. marcescens and the like.