Organic　mercury　including　methyl-mercury　and　ethyl-mercury　(CH3Hg+　and　C2H5Hg+)　has　high　toxicity　and　bio-accumulation,　and　thus　is　easy　to　generate　bio-amplification　in　food　chain.　Hence,　the　specific　detection　of　organic　mercury　has　great　significance　for　objectively　assessing　the　health　risk　of　mercury　in　seafood.　We　herein　designed　an　aptamer　(AS-T7),　which　consists　of　a　silver　nanoclusters　(AgNCs)　scaffold　sequence　(AS)　and　a　T-rich　sequence　(AT7),　for　simultaneously　synthetizing　DNA-templated　AgNCs　and　recognizing　organic　mercury,　and　further　developed　a　label-free　fluorescent　method　for　the　sensitive　and　specific　determination　of　organic　mercury　(CH3Hg+　and　C2H5Hg+　total　concentration)　by　using　DNA-templated　AgNCs　as　signal.　Without　organic　mercury,　Ag+　in　the　mixture　of　aptamer　and　Ag+　was　bond　on　AS　of　aptamer　to　form　AS-templated　AgNCs　after　reduction,　and　thus　emitted　strong　fluorescence.　Whereas,　in　the　presence　of　organic　mercury,　CH3Hg+/C2H5Hg+　was　bond　on　AT7　of　aptamer　to　generate　photoinduced　electron　transfer　(PET)　between　CH3Hg+/C2H5Hg+　and　AS-templated　AgNCs,　and　thus　results　in　fluorescence　quenching　of　AS-templated　AgNCs.　The　fluorescent　method　could　be　used　to　rapidly　detect　organic　mercury　with　a　detection　limit　of　5.0　nM　(i.e.　1.01　ng　Hg/g),　which　meets　the　U.S.　EPA　standard　of　0.3　mg/kg　(wet).　The　method　was　successfully　used　to　detect　organic　mercury　in　water　and　fish　muscle　with　a　recovery　of　96%–104%　and　an　inter-days　RSD　(n　=　5)　©　2021　Elsevier　B.V.