Electrochemical properties of ruthenium oxide (RuO2) films with different degrees of crystallinity were studied. The RuO2 films were grown by pulsed laser deposition at substrate temperatures from 30 to 400 degrees C. At low temperatures, the amorphous phase of RuO2 films was formed. At high temperatures, the crystalline phase of RuO2 films was obtained. From the cyclic voltammetric study in H2SO4 solution, it was found that the current response for an electrode of the amorphous RuO2 film was higher than that of the crystalline film. A proton diffusion length of larger than 5.8 nm was obtained on the RuO2 film prepared at 30 degrees C.