The effect of sodiumdiethyl dithiocarbamatetrihydrate (NaDDCT) on the corrosion of carbon steel in O2–saturated 0.25MH2SO4 solutions have been studied using the open circuit potential (OCP) and potentiodynamic polarization (PDP) techniques. The results of open circuit potential showed that slightly shifts toward positive direction with increasing the concentration of NaDDCT inhibitor due to form a layer protected film on the carbon steel surface. The potentiodynamic polarization (PDP) results referred to the NaDDCT as a good inhibitor in O2 - saturated acidic medium as well acts as a mixed-type inhibitor. The inhibition efficiency increases with increasing of concentration of NaDDCT to exceeds%96.55. The adsorption of the NaDDCT inhibitor on the electrode surface is well depended to on the Langmuir adsorption isotherm. The ΔGads values indicated that the adsorption of NaDDC on the surface of carbon steel spontaneously