Gold nanoparticles in the cores coated by non-porous silica shells (Au@nSiO(2)) and by porous silica shells (Au@pSiO(2)) were synthesized and used to catalyze the reduction and oxidation reactions to understand the influence of the structure of silica shells on their catalytic activity. Au@pSiO(2) nanoparticles well catalyze the reduction and oxidation reactions while Au@pSiO(2) nanoparticles are inactive for those reactions. The characterizations combining with catalytic reactions reveal that the porosity of silica shells is responsible for catalytic activity.