Magnetite nanoparticles were supported on carbon paste electrode and characterized by low scan rate voltammetry and electrochemical impedance spectroscopy (EIS) to obtain mechanistic information related to its oxidation and reduction in acid media. The voltammograms showed only one reduction and one oxidation peak for the supported magnetite, which were attributed to formation of ferrous ion and ferric oxide, respectively. Both peaks are fairly wide, indicating complex mechanisms. Using EIS, a mechanism showing up to three time constants, capacitive all of them, was evidenced, both in anodic and cathodic domain. These were attributed to charge transfer at the highest frequencies, adsorption of generated species at intermediate frequencies, and proton adsorption at low frequencies. Discussion about the nature of the adsorbed species and the concerned mechanism for each domain is developed. (C) 2010 Elsevier Ltd. All rights reserved.