This invention relates to novel 7-acylaminocephalosporanic acid derivatives and pharmaceutically acceptable salts thereof, of high antimicrobial activity, said novel derivatives having the formula ##STR1## wherein R.sup.1 is amino or protected amino,R.sup.2 is carboxy(lower)alkyl, protected carboxy(lower)alkyl, carboxy(lower)alkenyl, protected carboxy(lower)alkenyl, or lower unsaturated aliphatic hydrocarbon,R.sup.3 is hydrogen, halogen, methyl, lower alkoxy, lower alkylthiomethyl, lower alkanoyloxymethyl or a heterocyclicthiomethyl which may have suitable substituents(s),R.sup.4 is carboxy or protected carboxy,R.sup.5 is hydrogen or lower alkyl, andX is halogen,provided that when R.sup.3 is lower alkanoyloxymethyl, then R.sup.2 is lower unsaturated aliphatic hydrocarbon, and pharmaceutically acceptable salts thereof.