Infections caused by bacteria have a significant impact on public health. Chemical synthesis of new derivatives of cephalexin inked to amino acid (tryptophan or histidine) through an amide bond at the acyl side chain is achieved. This is a new approach of incorporating, tryptophan and histidine into the the primary amino group of cephalexin, in order to provide a bulky group very close to the β-lactam ring. This chemical addition act as isosteric group to the alkoximino that protect beta lactam ring from bacterial beta lactamase enzyme. The new derivatives may show resistance to β-lactamases, improve activity and pharmacokinetic properties and may give new life for old drugs that are susceptible to hydrolysis by most β-lactamases. The chemical structures of these derivatives were confirmed by: FTIR, 1H-NMR spectroscopy, elemental micro analysis and some physical properties. Molecular docking on serine beta lactamase and prediction of ADME parameters were recorded using GOLD suite and Swiss ADME software respectively. Docking scores of the new derivatives of Cephalexin on β-lactamases were higher than those of Cephalexin, which may indicate better activity