The effects of duration and temperature of hydrothermal ageing treatments were investigated on a commercial Fe-zeolite catalyst for NH3-SCR addressing NH3 adsorption, NH3 oxidation, and NH3 reaction with NOx. Hydrothermal ageing affected primarily NH3 oxidation and standard SCR activities, as well as NH3 storage capacity. Deactivation was fast in the first few hours, eventually approaching asymptotic levels. There is potential to predict the effects of hydrothermal ageing on the SCR behavior of Fe-zeolite catalysts as a function of just one parameter, i.e., the NH3 storage capacity.