A　modified　external　passivation　route　was　performed　to　control　the　distribution　of　gold　nanoparticles　in　periodic　mesoporous　organosilica　(PMOs).　The　surfactants　were　first　removed　completely　to　ensure　enough　space　in　the　mesopores.　The　external　surface　was　then　functionalized　with　n-octadecyltrimethoxysilane　(C18TMS),　and　finally　the　internal　surface　was　modified　with　aminopropyltrimethoxysilane　(APTMS)　to　enhance　the　adsorption　of　(HAuCl4)(-)　complex,　followed　by　the　reduction　under　hydrogen　atmosphere.　The　external　passivation　aims　to　prevent　the　formation　of　large　aggregated　gold　particles　on　the　exterior　surface.　The　aminopropyl　groups　at　the　internal　surface　ensure　the　incorporation　of　gold　nanoparticles　with　a　size　about　5　nm　inside　the　pore　channels　of　PMOs.　A　combination　of　high-resolution　TEM/STEM　and　SEM　shows　that　the　selective　surface　functionalization　can　effectively　avoid　the　growth　of　large　gold　particles　at　the　external　surface　and　strictly　confine　the　gold　nanoparticles　within　the　pore　channels　of　PMOs.　The　confined　gold　nanoparticles　in　PMOs　exhibit　good　catalytic　properties　in　the　reduction　of　methylene　blue　(MB)　dye　with　sodium　boron　hydride　as　reducing　agent.　(C)　2008　Elsevier　Inc.　All　rights　reserved.