Abstract: The inhibition effect of L-cysteine as environmentally friendly corrosion inhibitor for XC 18 carbon steel in stirred 2 N sulphuric acid has been investigated by electrochemical techniques. The impedance measurements showed that the inhibition efficiency increased with the increase of inhibitor concentration to reach more than 84% at 500 mg L-1 and indicated that the amino acid act as mixed type inhibitor, while the adsorption followed the Langmuir isotherm. Effect of temperature is also studied in the 30-60�C range. The values of adsorption free energy ( G0ads) and activation energies (Ea) reveal a physical adsorption of the inhibitor on the steel surface.