Carbon　based　dots　capped　tin　oxide　nanosheets　(SnO2/CDs)　were　synthesized　by　liquid　exfoliation　of　tin　oxide　(SnO2)　nanoparticles　in　the　presence　of　single-layer　carbon　based　(CDs).　The　obtained　SnO2/CDs　have　lateral　sizes　of　about　20–50　nm　and　heights　of　about　3–4　nm.　A　thin　layer　of　CDs　of　about　1–2　nm　in　thickness　are　presence　on　the　surface　of　the　SnO2　nanosheets.　The　SnO2/CDs　present　excellent　surface　enhanced　Raman　spectroscopy　(SERS)　activity　due　to　the　chemical　enhancement　(CM)　led　by　the　charge　transfer　between　SnO2/CDs　and　the　target　molecules.　The　enhancement　factor　(EF)　of　the　SnO2/CDs　is　1.42　×　105,　taking　rhodamine　6G　as　a　model　target　molecule.　The　SnO2/CDs　are　further　hybridized　with　silver　nanoparticles　(AgNPs)　using　an　in　situ　synthesis　method.　The　obtained　homogeneous　nano-hybrids　(SnO2/CDs@AgNPs)　have　a　lot　of　nanogaps.　The　nanogaps　among　the　AgNPs/CDs　create　strong　electromagnetic　enhancement　(EM)　due　to　the　＇hot　spots＇　effect.　The　nanogaps　among　the　SnO2/CDs　and　AgNPs/CDs　allow　the　target　molecules　to　be　embedded,　and　thus　gained　both　the　CM　effect　of　SnO2/CDs　and　the　EM　effect　of　AgNPs/CDs.　As　a　result,　the　as-prepared　SnO2/CDs@AgNPs　exhibits　excellent　SERS　activities,　with　an　ultrahigh　enhancement　factor　of　3.27　×　1011.　©　2020　Elsevier　Ltd