Encapsulation of Pt nanoparticles (1‐2 nm) in the small pore zeolite chabazite (CHA) was achieved by a seed‐ and structuredirecting agent‐free interzeolite transformation from zeolite Y (FAU). Prior to the transformation, the Pt nanoparticles were encapsulated in the commercially available large pore zeolite H‐Y by simple incipient wetness impregnation. The H‐Y was then converted into CHA in a solution of KOH under hydrothermal conditions at 95 °C. All catalysts were characterized by XRD, N2‐physisorption, H2‐chemisorption, TEM and XPS and their catalytic activity were tested in CO oxidation. Although the catalytic activity of the encapsulated Pt nanoparticles decreased over time, it still remained more active than a reference catalyst prepared by impregnation. The thermal stability of the catalysts was investigated after calcination at 400 °C for 18 hours. Compared to the other catalysts, the encapsulated Pt nanoparticles only resulted in a small decrease in catalytic activity.