The effect of an antibiotic ampicilin is studied for use as a low cost and ecofriendly corrosion inhibitor for mild steel in acidic environment. The corrosion inhibition effect is investigated using weight loss, Tafel polarization, electrochemical impedance spectroscopy and hydrogen permeation studies. The inhibitor showed 80% inhibition efficiency at 15x10-4M concentration of ampicillin. Potentiodynamic polarization suggests that it is a mixed type of inhibitor. Electrochemical impedance spectroscopy was used to investigate the mechanism of corrosion inhibition.Hydogen permeation__ampersandsignnbsp; easurements indicated that the compound behave as cathodic inhibitor ,but predominantly under mixed control. Diffused reflectance spectroscopy (DRS) studies confirmed only the mere adsorption of Ampcilin on mild steel surface and not influence on the surface morphology. he adsorption of this compound on mild steel surface obeys Temkin__ampersandsignlsquo;s adsorption isotherm.