A fluid catalytic cracking (FCC) catalyst is used in refineries to upgrade crude oil into valuable products. To fulfill the increasing demand for propylene, additives are used to boost propylene production. The hydrothermal conditions in a FCC unit gradually deactivate the Y-zeolite in the catalyst and the ZSM-5 zeolite in the additive by a dealumination of the framework structure. By powder X-ray diffraction, the change in the lattice parameter of the Y-zeolite over time is used to monitor the deactivation process. In this paper, we have shown that with a combination of powder X-ray diffraction and Rietveld analysis we can monitor the deactivation of ZSM-5. The lattice parameters measured for ZSM-5 are used to calculate the unit cell volume, which shows a good correlation with physical properties, such as total acidity and surface area, and the catalytic properties of ZSM-5 based additives. The data demonstrate that the technology can be applied to both laboratory and field deactivated ZSM-5 based additives.