The Inhibition of mild steel corrosion in well water 1,3-diethyl thiourea (DETU) has been reported by weight loss, electrochemical polarization technique, impedance method and quantum mechanical measurement. It was found that the compound effectively reduces the steel corrosion in the salt water medium. The inhibition efficiency (IE) increases as the inhibitor concentration is increased. Quantum mechanical studies confirm the adsorption of protective layer of inhibitor on mild steel surface.