Abstract: In order to investigate the effects of the N-substituents which the electron-withdrawing groups are far-away from the nitrogen atom of the β-lactam ring on the β-lactamases inhibition activities, twenty one title compounds have been synthesized from methyl p-amino-phenylacetate and p-amino-acetophenone. Condensation between "Dane Salt" and azomethines carrying an ester function or an acetyl group in the presence of ethyl chloroformate and triethylamine leads to stereo-specific synthesis of cis-3-enamino -2-azetidinones in about 10-50% yield. The 3-amino protective group can be easily removed with hydrochloric acid in 80～90% yield. The 3-amide-β-lactam-esters on treatment with 0.1N NaOH in acetone give a free carboxyl group in 50-70% yield without affecting the β-lactam ring or the amido side chain. The structure of these β-lactams were confirmed through their elemental analysis, IR, ¹HNMR and MS spectra. The β-lactamase inhibition activity test in vitro showed that fifteen title compounds carrying a free carboxyl function far-away from the ring nitrogen atom have inhibitory activity against two β-lactamases produced by P. aeruginosa, and Acetobacter respectively.