A citrate-stabilizing Au nanoparticles aqueous solution was prepared at near 0 oC by reducing tetracholoaurate(III) ions with sodium borohydride. Combining with Pluronic block copolymers, the citrate-stabilizing Au nanoparticles was nearly completely embedded in the mesoporous silica channels via fast silicification with silicate solution at near neutral pH. After calcination for removing organic templates, Au nanoparticles@mesoporous silicas of high surface area and pore volume were obtained. With different block copolymer, the pore size of the mesoporous silica can be tuned. The Au nanoparticles@SBA-15 mesoporous silica exhibits high catalytic activity to CO oxidation reaction.