Thin-film ruthenium oxide electrodes are prepared by cathodic electrodeposition on a titanium substrate. Different deposition periods are used to obtain different film thicknesses. The electrodes are used to form a supercapacitor with a 0.5M H2SO4 electrolyte. The specific capacitance and charge–discharge periods are found to be dependent on the electrode thickness. A maximum specific capacitance of 788Fg−1 is achieved with an electrode thickness of 0.0014gcm−2. These results are explained by considering the morphological changes that take place with increasing film thickness.