Emanation thermal analysis (ETA), thermogravimetry (TG), differential thermal analysis (DTA), X-ray diffraction analysis (XRD), and transmission electron microscopy (TEM) were used for the characterization of thermal behavior of hydrous oxides (RuO2)(x)-(TiO2)(1-x) (.) nH(2)O and dehydrated oxides (RuO2)(x)-(TiO2)(1-x), respectively (x =1, 0.9, and 0.7) on heating in argon and argon + 10% hydrogen, respectively. The samples were heated in the range 20-600degreesC at the constant heating rate 6 K/min. From the TG and DTA results the temperature intervals of dehydration and/or reduction of ruthenium dioxide into Ru metal were determined. ETA (based on the measurement of radon previously incorporated into the sample) brought about the information about surface area development and microstructure changes in the near surface layers up to 80 mm under in situ conditions of the heating. The temperature intervals of the annealing of near surface and structure defects serving as diffusion paths for radon were determined from the ETA results.