Abstract: The present invention relates to novel cephem compounds having the formula: ##STR1## wherein, Q is a carbon or nitrogen atom; X is an oxygen atom, or a nitroalkyl or cyanoimine group, with the proviso that X cannot be an oxygen atom when Q is a carbon atom; R.sub.1 is a hydrogen atom, or a lower alkyl group, or a lower alkyl group which may be substituted by fluoro, or by a carboxylic group or an inorganic cation salt thereof; and R.sub.2 and R.sub.3 independently are a hydrogen atom or a lower alkyl group; or pharmaceutically acceptable salts thereof.The compounds of the present invention have potent antibacterial activities against gram-negative bacteria, especially Pseudomonas, and a longer half-life than conventional cephem compounds.