The paper aims to provide some insight into the fundamental mechanisms for the behavior of cerium oxides nanoparticles as corrosion inhibitors for steel. The work was carried out on mild steel water based dispersions of cerium oxides nanoparticles in presence of both, sulfates and chlorides. Ceria nanoparticles were produced via precipitation of cerium Ce(NO3)(3).6H(2)O in water, particles of about 70 nm hydrodynamic diameter were obtained. The analysis of the effectiveness of the ceria nanoparticles as corrosion inhibitors was performed by means of electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) versus time measurements. The experimental measurements suggested that cerium oxide affects the electrochemical properties of mild steel surface; they promoted an ennoblement effect and strong modifications in the impedance response. (C) 2013 Elsevier Ltd. All rights reserved.