The dissolution mild steel in 1M H2SO4 has been retarded by Dicloxacillin (DCN) as corrosion inhibitor was investigated using weight loss, Potentiodynamic polarization, Electrochemical impedance spectroscopy, Hydrogen permeation and diffuse reflectance spectroscopic studies. All these techniques reveal that inhibition efficiency increases with increase in the concentration of DCN. Polarization studies indicated that Dicloxacillin behaved as cathodic inhibitor. Diffuse reflectance spectroscopy confirmed the adsorption of inhibitor on the mild steel surface obeying Langmuir adsorption isotherm. The quantum chemical analysis substantiates the inhibition efficiencies of the compound determined by electrochemical methods. © Int.J. ChemTech Res. 2015