In an integrated scheme for photochemical splitting of water to oxygen and hydrogen, there is a need for catalysts that couple the charge separated species to the redox reactions of water. Ruthenium oxide is well known as an efficient catalyst for photochemical four-electron oxidation of water to O 2 . Zeolites are an excellent host for creating longlived photochemically generated charge-separated species. There is a need for mild methods of incorporation of catalysts onto zeolites for water oxidation reactions. We report here that thermal decomposition of RU 3 (CO) 12 on zeolite Y at 170°C produces Ru metal which is readily oxidized to RuO 2 by air. The morphology of RuO 2 on the zeolite is strongly dependent on the temperature at which air oxidation occurs. Samples of RuO 2 -zeolite made by air oxidation at 200°C produce fibers of RuO 2 of approximate dimensions of length of 50 nm and widths of 5 nm. This material is found to be an efficient catalyst for oxidation of water to oxygen by photochemically generated Ru(bpy)3+ 3 in solution. This study demonstrates that a specific morphology of RuO 2 is optimum for an effective catalyst, thereby suggesting that particular crystal faces of RuO 2 provide catalytic sites.