Metallic　Au　nanoparticles　(NPs)　are　active　catalysts　in　many　chemical　reactions.　However,　small-size　Au　NPs　are　difficult　to　obtain　since　they　tend　to　agglomerate　due　to　their　high　surface　energies.　Herein,　we　reported　a　facile　and　green　hydrothermal　process,　using　graphene　oxide　(GO)　as　the　RGO　precursor,　HAuCl4　as　Au　precursor　and　L-cysteine　(L-cys)　as　both　cross-linker　and　reducing　agent,　to　fabricate　an　Au/RGO　composite　aerogel.　During　the　hydrothermal　process,　the　reduction　of　GO/HAuCl4,　the　oxidation　of　L-cys　to　produce　disulfide　linkage,　and　the　self-assembly　of　RGO　aerogel　occurs　simultaneously,　leading　to　the　resultant　RGO　aerogels　uniformly　and　in-timately　embedded　with　disulfide　protected　ultrasmall　Au　NPs　with　an　average　size　of　1.3　nm.　The　as-obtained　Au/RGO　composite　aerogel　exhibited　superior　catalytic　performance　for　reduction　of　4-nitrophenol　(4-NP)　to　4-aminophenol　(4-AP),　with　a　total　transformation　of　4-NP　achieved　in　4　min.　The　much　higher　activity　over　Au/　RGO　aerogel　as　compared　with　unsupported　thiol-capped　Au　NPs　can　be　attributed　to　the　synergistic　effect　of　metallic　Au　and　RGO.　Moreover,　Au/RGO　composite　aerogel　also　showed　high　stability　and　can　be　easily　separated　from　the　reaction　systems　for　recycling.　No　obvious　decrease　of　catalytic　reduction　activity　was　observed　over　the　Au/RGO　aerogel　after　five　cycles.　Considering　the　high　price　of　metallic　Au,　the　embedding　of　Au　NPs　in　three-dimensional　RGO　aerogels　to　facilitate　its　recycling　is　extremely　appealing　for　its　practical　applications.