RuO2-based mesoporous thin films of optical quality are synthesized from ruthenium-peroxo-based sols using micelle templates made of amphiphilic polystyrene-polyethylene oxide block copolymers. The mesoporous structure and physical properties of the RuO2 films (mesoporous volume: 30%; pore diameter: similar to 30 nm) can be controlled by the careful tuning of both the precursor solution and thermal treatment (150-350 degrees C). The optimal temperature that allows control of both mesoporosity and nanocristallinity is strongly dependent on the substrate (silicon or fluorine-doped tin oxide). The structure of the resulting mesoporous films are investigated using X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. Mesoporous layers are additionally characterized by transmission and scanning electron microscopy and ellipsometry while their electrochemical properties are analyzed via cyclic voltammetry. Thick mesoporous films of ruthenium oxide hydrates, RuO2 center dot xH(2)O, obtained using a thermal treatment at 280 degrees C, exhibit capacitances as high as 1000 +/- 100 F g(-1) at a scan rate of 10 mV s(-1), indicating their potential application as electrode materials.