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International audience; Metal oxides are important functional materials with a wide range of applications, especially in the field of electrocatalysis. However, quick and accurate assessment of their real electroactive surface area (ECSA), which is of paramount importance for the evaluation of their performance, remains a challenging task. In the presentation, I will present a relatively simple strategy for an accurate in situdetermination of the ECSA of commonly used metal oxide catalysts, namely: Ni-, Co-, Fe-, Pt-and Ir-based oxides. Similar to the well-established practice in electrocatalysis, the method is based on the phenomenon of specific adsorption. It uses the fact that,at the electrode potentials close to the onset of the oxygen evolution reaction (OER), specifically adsorbed reaction intermediates manifest themselves through so-called adsorption capacitance, which is unambiguously detectable using electrochemical impedance spectroscopy.[1,2] With simple impedance measurements, experimentalists can acquire the adsorption capacitance values and accurately estimate the real electroactive surface area of the above-mentioned oxide materials, including nanostructured electrocatalysts. Additionally, as illustrative examples, I will demonstrate an application of the method for the determination of the ECSA of oxide catalyst nanoparticles.