This invention relates to the preparations of noble metal catalysts, i.e., platinum and platinum alloys, on suitable supports with nanonetwork structures and high catalytic efficiencies. A compact structure of a monolayer or a few layers is formed by self-assembly of organic polymer, e.g., polystyrene (PS), nanospheres or inorganic, i.e., silicon dioxide (SiO.sub.2), nanospheres on a support surface. In the void spaces of such a compact arrangement, catalyst is formed by filling with catalyst metal ion-containing aqueous solution and reduced by chemical reduction, or formed by vacuum sputtering. When using organic polymer nanospheres as the starting or structure-directing material, the polymer particles are removed by burning at a high temperature and the catalyst having a nanonetwork structure is obtained. In the case of using silicon dioxide nanospheres as the starting material, silicon dioxide particles are dissolved with hydrofluoric acid solution and evaporated away leading to formation of a similar nanonetwork structure made of catalyst. The catalysts prepared by these methods possess characteristics of robust in structure, uniform in hole size and high in catalytic surface area. Their main applications include uses as catalysts in direct methanol and proton exchange membrane fuel cells, as well as in chemical reactors, fuel reformers, catalytic converters, etc.