New cyanomethylthioacetylcephalosporins of the following general formula, and their salts ##SPC1##Wherein R is hydrogen or a salt forming ion of the group consisting of aluminum, alkali metal, alkaline earth metal, lower alkylamine, phenyl-lower alkylamine, N,N'-dibenzylethylenediamine, procaine or lower alkylpiperidine; R.sub.1 and R.sub.2 each is hydrogen, lower alkyl, lower alkenyl, phenyl, hydroxyphenyl, chlorophenyl, benzyl, phenethyl or R.sub.1 and R.sub.2 together complete a cyclopentyl or cyclohexyl group; R.sub.3 is cyclo-lower alkyl, cyclo-lower alkenyl or cyclo-lower alkadienyl; and X is hydrogen, lower alkanoyloxy, lower alkoxy or lower alkylthio.