Methyl-mercury　(CH3Hg+)　and　ethyl-mercury　(C2H5Hg+)　have　much　higher　toxicity　than　Hg2+　and　can　be　more　easily　accumulated　by　organisms　to　form　severe　bioamplification.　Hence,　the　specific　and　on-site　detection　of　CH3Hg+　and　C2H5Hg+　in　seafood　is　of　great　significance　and　a　hard　challenge.　We　herein　designed　two　T-rich　aptamers　(HT5　and　HT7)　for　specifically　recognizing　CH3Hg+　and　the　total　of　CH3Hg+　and　C2H5Hg+,　respectively.　In　the　presence　of　all　Au3+,　Ag+,　and　T-rich　aptamer,　CH3Hg+　and　C2H5Hg+　specifically　and　preferentially　bind　with　aptamer　and　thus　induced　the　formation　of　alloy　Ag-Au　nanoparticles　after　reduction,　which　led　to　the　color　change　in　solution.　This　provided　a　sensing　platform　for　the　instrument-free　visual　discrimination　and　detection　of　CH3Hg+　and　C2H5Hg+.　By　using　HT5　as　probe,　the　method　can　be　used　to　detect　as　low　as　5.0　μM　(equivalent　to　1.0　μg　Hg/g)　of　CH3Hg+　by　bare　eye　observation　and　0.5　μM　(equivalent　to　100　ng　Hg/g)　of　CH3Hg+　by　UV-visible　spectrometry.　By　using　HT7　as　probe,　the　method　can　be　used　to　detect　the　total　concentration　of　CH3Hg+　and　C2H5Hg+　with　a　visual　detection　limit　of　5.0　μM　(equivalent　to　1.0　μg　Hg/g)　and　a　UV-visible　spectrometry　detection　limit　of　0.6　μM　(equivalent　to　120　ng　Hg/g).　The　proposed　method　has　been　successfully　used　to　detect　CH3Hg+　and　C2H5Hg+　in　fish　muscle　samples　with　a　recovery　of　101-109%　and　a　RSD　(n　=　6)　<　8%.　The　success　of　this　study　provided　a　potential　method　for　the　specific　and　on-site　detection　of　CH3Hg+　and　C2H5Hg+　in　seafood　by　only　bare　eye　observation.　©　2018　American　Chemical　Society.