This invention provides a penam derivative represented by the formula ##STR1## wherein R is hydrogen or methyl and R.sub.1 is (hexahydro-1H-azepin-1-yl)methyleneamino, 2-phenylacetamido, 2-phenoxyacetamido, 2-amino-2-phenylacetamido, 2-amino-2-(p-hydroxyphenyl)acetamido or 2-(4-ethyl-2,3-dioxo-1-piperazine)carboxamido-2-phenylacetamido, and a salt thereof, and processes for preparing them.