The inhibition effect of a new synthesized Schiff base, namely 4-nitro-2-methoxy phenyl- N-salicylidine on the corrosion of mild steel in 0.5 M HCl acid have been investigated at room temperature using electrochemical impedance spectroscopy(EIS), Tafel polarization and weight loss measurements. It was concluded that the inhibition efficiencies increased with increase in the concentrations of the Schiff base. The inhibition efficiencies obtained from all methods employed are in good agreement with each other. Tafel polarization studies showed that the Schiff base was mixed type inhibitor. The adsorption of this compound on a mild steel surface from 0.5 M HCl acid obeyed the Langmuir adsorption isotherm and the thermodynamic calculations revealed that the adsorption of inhibitors was of physical nature.