Cyclic voltammetry was used in order to directly deposit hydrous ruthenium oxide (RuO x ·nH 2 O) on conductive diamond substrates. It was found that, at the hydrogen-terminated boron-doped diamond (BDD) surface, the overall deposition process is rather slow compared to the case of metal substrates. Nevertheless, the values estimated for the specific charge and specific capacitance by cyclic voltammetric and chronopotentiometric experiments, respectively, compare favorably to those reported in the literature. Additional advantages of using a BDD support are the excellent stability of the response, the extreme robustness even under severe functioning conditions, and, importantly, negligible substrate effects. It was also observed that RuO x ·nH 2 O deposition at a BDD powder surface greatly enhanced both the specific charge and the specific capacitance. These features strongly recommend the use of conductive diamond powder as a substrate for hydrous ruthenium oxide, particularly in view of possible, electrochemical capacitor applications.