Effects of temperature and pH of the plating baths, potential ranges and scan rates of cyclic voltammetry, and concentrations of RuCl3. xH(2)O on the deposition rate and the physicochemical properties of hydrous ruthenium oxide (i.e. RuOy. nH(2)O) are investigated systematically. For the RuOy. nH(2)O deposition, the apparent reaction order of RuCl3. nH(2)O is 1 while effects of pH are very complicated, probably due to the influence on the structure of the dissolved chloro-hydroxyl-ruthenium species, rendering a change in deposition mechanism. The redox transitions of oxyruthenium species between different oxidation states within the RuOy. nH(2)O deposits are electrochemically reversible while the electrodes covered with a very thin RuOy. nH(2)O film exhibit a less reversible characteristic. Surface morphologies and crystalline information of these RuOy. nH(2)O deposits are examined by scanning electron microscopy and X-ray diffraction, respectively.