Thermal deactivation and structural specificity of V2O5/TiO2 catalyst were investigated in the selective catalytic reduction of nitric oxides. Catalysts were characterised by BET specific surface area technique, mercury penetration porosimetry, X-ray diffraction and scanning electron microscopy. A steady state fixed bed reactor with the appropriate measurement system was used for the activity tests of original and thermally deactivated catalyst samples. The 72 hour heat treatment at the temperature of 420 and 480 degrees C has not significant effect on the bulk density, density, pore volume and phase composition of catalyst. The surface area of samples decreased characteristically. The relation of reaction rate preexponent constant to the specific surface area can be used as a measure of deactivation.