The corrosion inhibition of mild steel in 0.5 M HCl by a coupling reagent, 1-(3-Pimethylaminopropyl) 3-ethylcarbodiimide hydrochloride ( EDC), has been investigated by weight loss, electrochemical impedance spectroscopy (EIS), polarization technique, theoretical studies of quantum chemistry and scanning electron microscopy (SEM). Experimental results show that the reagent is an effective inhibitor for the corrosion of mild steel in acidic solution and it exhibited > 90% inhibition efficiency at low concentrations of the inhibitor. Potentiostatic polarization studies show that the studied compound is a mixed-type inhibitor. The results of EIS show that EDC inhibits corrosion of mild steel by adsorption mechanism. Surface morphology has been studied by SEM and the theoretical quantum calculations also are in agreement with the experimental results. The adsorption of inhibitor on the mild steel surface follow Langmuir adsorption isotherm. The thermodynamic parameters of corrosion process have also been calculated and discussed.