Abstract: The invention relates to new cephem compounds of high antimicrobial activity of the formula: ##STR1## wherein R.sup.1 is amino or a group of the formula: ##STR2## in which R.sup.5 is amino or a protected amino group,R.sup.9 is lower alkyl, lower alkenyl, lower alkynyl, cyclo(lower)alkenyl, carboxy(lower)alkyl, protected carboxy(lower)alkyl or saturated 4 to 8-membered heteromonocyclic group containing one sulfur atom, andZ is N or CH,R.sup.2 is cyano, phenyl, pyridyl, lower alkylpyridyl, or tri(lower)alkylsilyl,R.sup.3 is carboxy or protected carboxy, andA is --CH.dbd.CH-- or --C.tbd.C--,and pharmaceutically acceptable salt thereof.

Abstract: A 2-substituted cephem derivative represented by the formula ##STR1## wherein R.sup.1 represents a substituted or unsubstituted phenyl group, substituted or unsubstituted phenylmethyl group or substituted or unsubstituted phenoxymethyl group, R.sup.2 represents hydrogen atom or protective group for carboxylic acid and Y represents allyloxy group, benzyloxy group, alkylthio group, carboxyalkylthio group or group of the formula ##STR2## wherein R.sup.4 represents hydrogen atom or lower alkyl group, X represents --O--, --S-- or ##STR3## R.sup.5 represents hydrogen atom, a lower alkyl group or phenyl group and R.sup.6 represents hydrogen atom or lower alkyl group, and a process for preparing the derivatives.