The influence of 1-0-Tolyl-3,3 diethyl thiourea (TDETU) on corrosion of mild steel in marine water (5% NaCl) has been studied using weight loss measurements and various electrochemical techniques. The compound inhibited the steel corrosion in salt water. Potentiodynamic polarization studies clearly indicated that TDETU behaved as a cathodic inhibitor. Electrochemical impedance spectroscopy was used to investigate the mechanism of corrosion inhibition. A chemdraw 3D simulation technique used to run the quantum mechanical analysis and established correlation's between different types of descriptors and measured corrosion inhibition efficiency for the compound. The use of this method substantiates the inhibition efficiencies of the compounds determined by electrochemical methods. AFM studies confirmed that the adsorption of the inhibitor reduces surface roughness on mild steel.