The structure of adsorption sites of highly dispersed oxides, such as TiO2, Fe2O3, and ZnO, was investigated by means of H2Se adsorption. The nanoparticles were studied with a specific surface area not less than 50 m(2)/g. The oxide surface was activated either by mechanical activation or by high temperature treatment in a gas flow. Irreversible H2Se adsorption was carried out up to saturation in H-2 excess at room temperature. EXAFS spectra of the Se-K edge were measured and analyzed. The ratio between point and extended defects as a function of the activation conditions was determined for TiO2, It was shown that oxygen, being removed from the Fe2O3 surface during the activation, is not associated with the presence of a cation in the interstitial positions. It was shown for ZnO that a change in the ratio between cation and anion vacations depends on the duration of the mechanical treatment. Perspectives of this approach and possibilities of using the probes are described.