For the selective catalytic reduction (SCR) of nitrogen oxides (NOx) from lean burn diesel engines, NH3 is used as reducing agent. In the case of V2O5-WO3 catalysts supported on TiO2 (anatase) ceramics, an adsorption of NH3 on the catalyst surface is required for the SCR reactions. To effectively control the NH3 supply and to obtain detailed knowledge on the catalyst status, it is crucial to know the current adsorbed amount of ammonia on the catalyst. It is shown for the first time in this study that it is possible to determine the ammonia loading of V2O3-WO3 catalysts contactless and in operand by a simple microwave-based approach. This method can be applied for different temperatures. It is possible to determine the stored amount of ammonia independently on the ammonia-to-NOx feed ratio. (C) 2014 Elsevier B.V. All rights reserved.