Corrosion inhibition of Cu-30Ni alloy in aerated 0.5 M H2SO4 solution by cysteine, an amino acid, has been investigated. Potentiodynamic polarization and impedance spectroscopy (EIS) at open circuit potential were performed. Corrosion current density was also determined from colorimetric experiments. Voltammetric curves showed that cysteine addition to 0.5 M H2SO4 affects largely the cathodic process; shifting the corrosion potential to more negative values and decreasing significantly the corrosion current density. The inhibiting efficiency reaches a value of 91% at an inhibitor concentration of 10(-3) M. Impedance data reveal the adsorption of the inhibitor and the surface relaxation process due to nickel. Polarization resistance deduced from impedance measurements or voltammetric experiments are in a good agreement. (C) 2009 Elsevier B.V. All rights reserved.