The　great　harm　of　thiram　residue　in　soil　to　environment　and　human　health　is　usually　ignored.　Due　to　the　complexity　of　soil　compositions,　the　detection　of　thiram　residue　in　soil　faces　considerable　difficulties.　In　this　work,　a　highly　sensitive　and　selective　surface-enhanced　Raman　scattering　(SERS)　substrate　based　on　the　triangular　silver　nanoplates　(TSNPs)　with　small　size　and　sharp　corners　is　developed　and　used　for　the　detection　of　thiram　residue　in　soil　for　the　first　time.　These　TSNPs　are　synthesized　by　replacing　the　conventional　seeds　in　the　seed-mediated　chemical　reduction　route　with　the　tiny　and　uniform　triangular　silver　nuclei　(TSN)　which　can　provide　more　growing　space　for　generating　sharp　corners　during　the　growth　of　TSNPs.　It　is　interesting　that　the　TSNPs　with　the　smaller　size　have　the　better　SERS　performance.　The　possible　mechanism　behind　this　phenomenon　is　explained　by　the　electromagnetic　enhancement　theory.　On　the　basis　of　the　Raman　activity　of　the　smallest　TSNPs,　a　SERS-active　substrate　is　prepared　for　detecting　the　thiram　residue　in　soil.　The　thiram　solution　detection　shows　that　the　limit　of　detection　(LOD)　of　these　smallest　TSNPs　is　lower　than　other　nanoparticles,　such　as　nanospheres,　nanocubes,　etc.　For　sensing　the　thiram　residue　in　soil,　the　addition　of　poly(sodium　4-styrenesulfonate)　realizes　the　specific　adsorption　of　thiram　by　TSNPs.　This　method　exhibits　a　good　linear　response　from　0.12　to　4.8　mu　g/g　with　a　low　LOD　of　90　ng/g,　which　is　better　than　conventional　methods.　This　work　shows　the　great　potential　of　the　small　TSNPs　as　a　novel　SERS　substrate　and　its　broader　applications　in　pesticides　detection.