Electrochemical impedance spectroscopy (EIS) and d.c polarization resistance measurements (Rp) were used to study the corrosion resistance of surface layers produced by nitrogen ion implantation into copper substrates. Ion implantation was carried out using a Wickham ion beam generator, applying an acceleration voltage of 100keV, a mean current of 0.40 mA and a nitrogen dosage of 4 × 1017 ions cm−2. Surface analyses were made by Auger electron spectroscopy (AES). Electrochemical measurements (EIS and Rp) performed in a 0.6m sodium chloride solution show nitrogen-implanted specimens have greater a.c. and d.c. apparent polarization resistance than nonimplanted specimens. The results obtained with electrochemical measurements indicate that nitrogen ion implantation in copper forms a protective surface layer which improves the corrosion resistance of the pristine material, a feature of great interest for the design of new contact materials for the electricity and electronic industries.