Zeolite-encapsulated molecular forms of rhenium oxide offer the opportunity to tune the physico-chemical properties of the materials due to the wide range of oxidation states available to rhenium (+7--1). This can lead to nanomaterials with interesting electronic, optical, and catalytic proper ties. Here, the encapsulation, structural characterization: thermal and chemical stability of CH3ReO3 in both sodium and acid forms of zeolite Y are reported.