Cancer　metastatic　spread　is　life-threatening　and　caused　by　circulating　tumor　cells　(CTCs)　that　are　very　difficult　to　precisely　capture　in　vivo.　Here　we　show　that　two　aptamer　rings　targeting　different　CTC　biomarker　epitopes　conjugated　on　dendrimers　capture　CTCs　with　enhanced　precision　even　in　the　presence　of　108　interfering　cells,　or　blood　cells,　and　in　mice　or　patient　samples　when　compared　with　their　single　aptamer　counterparts.　The　aptamer-conjugate　inhibited　in　vivo　metastasis　and　demonstrated　enhanced　biostability　by　resisting　biodegradation　caused　by　the　endogenous　nucleases.　The　capture　arms　of　the　aptamer　conjugates　could　simultaneously　and　specifically　seize　two　biomarkers　(EpCAM　and　Her2).　The　double　seizure　resulted　in　significant　cell-cycle　arrest,　apoptosis,　and　growth　inhibition　of　the　captured　CTCs.　The　aptamer-conjugate　highly　penetrated　and　accumulated　in　mouse　tumors.　This　study　provides　the　first　conceptual　evidence　that　two　aptamer　rings,　inexpensive　but　bioequivalent　to　their　antibodies,　can　be　biocompatibly　conjugated　to　specifically　capture　and　down-regulate　CTCs　in　vivo　with　the　enhanced　biostability.　©　2017　American　Chemical　Society.