V₂O₅/WO₃-TiO₂ selective catalytic reduction (SCR) catalysts with a V₂O₅ loading of 1.7, 2.0, 2.3, 2.6, 2.9, 3.2 and 3.5 wt. % were investigated in the fresh state and after hydrothermal aging at 600 °C for 16 h. The catalysts were characterized by means of nitrogen physisorption, X-ray diffraction and X-ray absorption spectroscopy. In the fresh state, the SCR activity increased with increasing V loading. Upon aging, the catalysts with up to 2.3 wt. % V₂O₅ exhibited higher NO_x reduction activity than in the fresh state, while the catalysts with more than 2.6 wt. % V₂O₅ showed increasing deactivation tendencies. The observed activation and deactivation were correlated with the change of the VO_x and WO_x surface coverages. Only catalysts with a VO_x coverage below 50% in the aged state did not show deactivation tendencies. With respect to tungsten, above one monolayer of WO_x, WO₃ particles were formed leading to loss of surface acidity, sintering, catalyst deactivation and early NH₃ slip. An optimal compromise between activity and hydrothermal aging resistance could be obtained only with V₂O₅ between 2.0 and 2.6 wt. %.