We report the synthesis, using an organic-template-free hydrothermal crystallization method, and catalysis of a new type of nanocomposite material, 1.3 nm-sized RuO₂ particles confined in faujasite zeolite. The zeolite-confined RuO₂ composites were fully characterized with X-ray powder diffraction, Ru K-edge X-ray absorption, and high-resolution transmission electron microscopy. XRD and X-ray fluorescence analysis indicate that the framework is faujasite zeolite with a Si:Al ratio of 1.25. Ru K-edge X-ray absorption near-edge structures indicate that the ruthenium species in the zeolite is Ru(IV) with nearest-neighbor octahedral environments similar to hydrous RuO₂, i.e., distorted "RuO₆". The k²-weighted extended X-ray absorption fine structure indicates that the Ru(IV) species anchored in the zeolite likely form amorphous RuO₂ with a 2D-chain structure, in which RuO₆ units are connected together by two shared oxygen atoms. TEM shows that the particle size of RuO₂ encapsulated inside the supercages of FAU is about 1.3 nm. The RuO₂–FAU composites display significant catalytic activity in the oxidation of cyclohexane with tBHP under mild (room temperature and 1 atm (1 atm [Formula: see text] 101.325 kPa)) conditions. The ketone and alcohol concentration can be as high as 0.26 mol L^–1 in 5 h with 48% peroxide efficiency. The catalyst is stable and reusable. Possible oxidation mechanisms are also discussed.Key words: nanocomposite, ruthenium oxide, catalysis, oxidation, zeolite.