Inhibitionperformance of sodium diethyidithiocarbaminat trihydrat (SDDT) against corrosion on mild steel (MS) in 0.5M HCl solution investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) methods. The inhibition efficiency increased with increasing of inhibitor concentration. The potentiodynamic polarization results indicated that all the studied inhibitors act as mixed type. SDDT adsorption on the MS surface obeyed the isotherm of Langmuir and the thermodynamic parameters; K ads , ∆G ○ ads were also calculated and discussed.