The electrochemical and textural characteristics of various hydrous ruthenium-iridium oxides (denoted as (Ru + Ir)O-x. nH(2)O) grown by cyclic voltammetry (CV) were systematically studied for the application of electrochemical (EC) capacitors. The faradaic pseudocapacitance of (Ru+Ir)O-x. nH(2)O reached the maximum when the depositing solution contained 5 mM RuCl3. xH(2)O and 1 mM IrCl3. xH(2)O. The linear dependence of C-cp on C-q* measured respectively by chronopotentiometry (CP) and CV at various (Ru + Ir)O-x. nH(2)O deposits was found to be independent of the compositions of oxides. The intercalation of IrOx. H2O within the RuOx. nH(2)O matrix promoted the utilization of electroactive oxyruthenium species while the presence of IrCl3. xH(2)O depressed the rate of (Ru + Ir)O-x. nH(2)O deposition. These effects were further supported by the textural results of these binary hydrous oxides examined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).