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　intimately　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.　©　2020　Elsevier　Ltd.