The catalytic properties of PdO/delta-Al2O3 catalysts prepared by hot isostatic pressing (HIP) have been investigated, The HIP treated catalysts (HIPed catalysts) showed higher catalytic activity for the oxidation of methane in the temperature range 973-1173 K than the catalysts calcined in atmosphere (non-HIPed catalysts). These catalysts were characterized by thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, CO adsorption and temperature-programmed desorption of oxygen. It was found that the palladium oxide stable against reduction was formed by the HIP treatment, and that oxygen in the HIP atmosphere played an important role for the formation of the stabilized palladium oxide species, The temperature dependence of catalytic activity was explained in connection with the palladium oxide species on the support.