Herein,　we　propose　a　selective　and　simple　colorimetric　sensing　approach　for　the　determination　of　Hg2+　ions　based　on　bimetallic　AuAg　nanocages　with　partial　hollow　cavity　and　several　pinholes　on　the　wall,　wherein　the　residual　Ag　atoms　existing　inside　this　AuAg　nanocages　can　be　directly　etched　by　Hg2+　and　the　generated　Hg　depositing　on　inner　surface　of　nanocages　induces　the　morphology　transformation　from　hollow　AuAg　nanocages　to　closed　nanoboxes　which　consists　of　an　AuAg　shell　and　Hg　core.　This　morphology　transformation　of　＇nanocage-to-nanobox＇　not　only　extends　the　detection　range　of　Hg2+,　but　also　cleans　the　Hg2+　in　solutions　by　enriching　it　into　the　nanoboxes.　With　increasing　Hg2+　concentrations,　the　blue　shift　of　localized　surface　plasmon　resonance　(LSPR)　peak　position　with　multicolor　changing　from　light-blue　to　light-brown　is　great　for　colorimetric　determination　of　Hg2+.　Under　optimal　conditions,　the　colorimetric　sensing　shows　a　linear　response　to　Hg2+　ranging　from　0.03　to　35　μM　with　a　detection　limit　of　10　nM.　Besides,　interference　study　and　real　samples　detection　applying　lake　and　tap　water　demonstrated　that　Hg2+　can　be　specifically　and　practically　detected　by　utilizing　this　method.　©　2020　Elsevier　B.V.