Hydrazono penicillin derivatives of the formula ##STR1## wherein R represents phenyl optionally substituted, 2- or 3- thienyl optionally substituted, or 2- or 3-furyl optionally substituted, R.sub.1 represents hydrogen, alkyl containing from 1 to 4 carbon atoms, or phenyl, and R.sub.2 represents hydrogen, pivaloyloxymethyl, or 1-(ethoxycarbonyloxy)ethyl radical. The compounds have antibacterial activity against gram-negative and gram-positive microorganisms. Methods of preparation are also disclosed.