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The use of cerium oxide nanoparticles as a corrosion inhibitor for the CO2 corrosion of LDX 2101 duplex stainless steel has been evaluated using potentiodynamic polarization curves, linear polarization resistance and electrochemical impedance spectroscopy tests. Polarization curves have shown that CeO2 nanoparticles behaved as an efficient mixed type of inhibitor, with an efficiency that increases with its concentration reaching a maximum value when 600 ppm of nanoparticles were added. CeO2 nanoparticles were chemically adsorbed onto the steel surface according to a Langmuir type of adsorption isotherm. A passive layer was formed by the addition of CeO2 nanoparticles with lower passive current density and higher pitting potential values than those obtained without these nanoparticles. Corrosion current density decreased whereas the polarization resistance increased by two orders of magnitude in both cases with the addition of the nanoparticles. Similarly, the double layer capacitance was decreased due to the adsorption of the nanoparticles. Steel was susceptible to pitting type of corrosion, but its number and diameter decreased with the nanoparticles.