The structure, strain and defects in epitaxial silicon carbide (SiC) thin films on aluminum nitride/sapphire (AlN/Al2O3), silicon (Si), titanium carbide (TIG) and 6H-SiC substrates were analyzed by X-ray diffraction, X-ray double crystal diffractometry and X-ray topographic techniques. The SiC thin films were confirmed to be epitaxials with a zinc blende structure when grown on Si, TiC and vicinal 6H-SiC, and a wurtzite 6H polytype structure when grown on AlN/Al2O3. The dislocation densities in the SiC films are in the order of 10(8) to 10(11) and are comparable. The experimental stress agrees well with the theoretical one calculated from the thermal expansion coefficient mismatch between the film and the substrate. X-ray rocking curves and X-ray topographs suggest that considerable amount of defects were generated in the Si substrates during the thin film growth process whereas the sapphire substrates remain defect free.