The adsorption and inhibitor effect of Expired Amoxicillin (E.A) on mild steel in 1 N HCl was studied by weight loss, potentiodynamic polarization, Electrochemical Impedance Spectroscopy (EIS), zero-charge potential method (PZC) and characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The inhibition efficacy obtained by gravimetry is 94.47% at 1800 ppm after 8 h immersion. Amoxicillin acts as a mixed inhibitor. The surface is negatively charged. E.A adsorption on mild steel surface obeys Langmuir isotherm, with a spontaneous process, the E.A molecules are physisorbed.