Highly conducting epitaxial RuO2 films with a thickness of 0.5 mum were grown by metal-organic chemical vapour deposition on (1 0 0) Si and (1 (1) over bar 0 2)-oriented Al2O3 single crystal substrates. Different structure was observed for the RuO2 films on these substrates; the films on Si substrate were polycrystalline, while X-ray diffraction analysis revealed epitaxial growth of RuO2 on the Al2O3 substrates, Electrical properties (room-temperature resistivity and residual resistivity ratio) of the RuO2 films were studied in connection with their preparation conditions, structure and morphology. Epitaxial RuO2 films on (1 (1) over bar 0 2)-oriented Al2O3 single crystal substrates exhibit low resistivity at room temperature rho(300) congruent to 30 muOmega cm and residual resistivity ratio up to 30. Moreover, the residual resistivity ratio of the RuO2 films on the Al2O3 substrate can be increased by additional annealing in oxygen atmosphere to the value as high as 60. (C) 2002 Elsevier Science B.V. All rights reserved.