A sample of 1%Au-0.5%Fe/HY was prepared by co-exchange in HY zeolite using iron(Il)ethylenediammonium and Au(III)ethylenediamine complex-ions. Highly stable gold nanoparticles inside zeolite supercages were formed by autoreduction. Monometallic gold and iron samples were also prepared by ion exchange. Xe-129 NMR and TEM studies revealed the presence of metallic gold nanoparticles along with iron cations inside the zeolite supercages. Neither the presence of metallic Au nor iron can be detected by X-ray photoelectron spectroscopy which is indicative of the presence of both metals inside the zeolite cavities. In the CO oxidation, the Au-Fe/Hy sample possessed the highest activity.