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The synergistic inhibitive effect of cysteine(Cys)and iodide ions on the corrosion behavior of copper was examined in a 0.5 mol·L-1 Na2SO4 solution.Poten-tiodynamic polarization curve revealed that Cys acted as a mixed type inhibitor with a major effect on the cathodic process,consequently decreased the corrosion current density by a great extent and shifted the corrosion potential negatively.The investigated results suggested that iodide ions can enhance the inhibition efficiency of Cys.The inhibition mechanism of Cys and the synergistic effect of the two examined reagents were investigated by fitting experimental impedance data according to a projected equivalent circuit for metal/electrolyte interface.Surface analysis further confirmed that the corrosion inhibition was realized due to the adsorption of the inhibitor molecules at the metal/solution interface.Langmuir adsorption isotherm was proposed to describe inhibition mechanism of Cys on copper surface.Active sites of Cys molecule were used to form inhibitor film on the copper surface.Addition of iodide ion increased its inhibition efficiency by enhancing adsorption of Cys cations through electrostatic interaction with I-pre-adsorbed on Cu surface.