The synthesis and some biological properties of $7{eta} $-[2-(Z)-(2-aminothiazole-4-yl)-2-(N-substitutedcar bonyl)ethoxyiminoacetamido]-3-vinyl-3-cephem-4- carboxylic acid are described. The effect of substituents on the carbamoly group in the 7-side chain were investigated in order to improve antibacterial activities. Two of these new orally active $7{eta} $-lactam derivatives showed wide expanded antimicrobial activities against Gram-positive and Gram-negative bacteria, including Pseudomonas aeruginosa, as well as good stability to $7{eta} $ -lactamases.