A　fast,　sensitive　and　high-resolution　colorimetric　method　for　sensing　benzoyl　peroxide　(BPO)　was　proposed　by　using　orange　sheath-like　Au@Ag　nanorods　(NRs)　as　the　signal　transducer.　BPO　can　oxidize　Ag　nanoshells　on　the　surface　of　Au@Ag　NRs;　the　etching　of　Ag　nanoshells　changes　the　aspect　ratio　of　Au　nanostructures　and　causes　a　red-shift　of　longitudinal　local　surface　Plasmon　resonance　(LSPR)　peak,　resulting　in　a　sharp-contrast　multicolor　change　within　2　min.　Under　the　optimal　conditions,　the　red-shift　of　longitudinal　LSPR　peak　was　in　linear　with　the　BPO　concentration　over　the　range　of　0–100　μmol　L−1　with　a　limit　of　detection　of　0.75　μmol　L−1.　Furthermore,　a　simple,　inexpensive　and　portable　test　kit　was　designed　for　the　visual　detection　of　BPO.　A　color　variation　can　be　distinguished　by　naked　eyes　at　a　concentration　of　BPO　as　low　as　20　mg　kg−1　in　flour　samples.　The　colorimetric　sensor　shows　a　great　potential　application　for　the　rapid　and　on-site　assay　of　BPO　in　flour　samples.　©　2018　Elsevier　B.V.