3-Deacetoxy-7-(α-amino-1-cyclohexenylacetamido) cephalosporanic acid (SCE-100) has a potent antibacterial activity against Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration of SCE-100 is 0.2-12.5μg/ml against Gram-positive bacteria including penicillin G-resistant Staphylococcus aureus and 6.25-100μg/ml against Gram-negative bacteria. SCE-100 inhibits clinically isolated strains of penicillin G-resistant S. aureus and ampicillin-resistant Escherichia coli, as well as the corresponding sensitive strains. The activity of SCE-100 is enhanced by decreasing the inoculum size and is only slightly influenced by medium pH, difference of medium composition and the addition of horse serum. SCE-100 has bactericidal activity against S. aureus and E. coli. There is a stepwise development of in vitro bacterial resistance to SCE-100 by serial transfer of organisms into a liquid medium containing SCE-100. Cross resistance was observed between SCE-100 and other tested cephalosporins.