A　novel　highly　active　surface　enhanced　Raman　scattering　(SERS)　substrate　of　Ag　nanoparticles　decorated　Ag@ZrO2　composite　nanosphere　was　prepared　and　characterized.　A　uniform　ZrO2　shell　was　firstly　coated　over　Ag　cores　by　sol-gel　process　using　zirconium　butoxide　as　Zr　precursor　to　achieve　Ag@ZrO2　nanospheres　and　then　Ag　nanoparticles　were　in　situ　deposited　on　the　Ag@ZrO2　through　the　reduction　of　AgNO3　to　produce　Ag@ZrO2@Ag　composite　nanospheres.　The　cover　density　of　Ag　nanoparticles　on　Ag@ZrO2@Ag　nanospheres　could　be　controlled　by　changing　the　concentration　of　AgNO3.　TEM,　FE-SEM,　EDX,　UV-vis　and　XRD　analyses　were　used　to　characterize　their　morphology,　structure　and　composition.　The　SERS　property　of　Ag@ZrO2@Ag　was　evaluated　using　4-mercaptobenzoic　add　(4-MBA)　as　Raman　probe　molecules.　The　experimental　results　showed　Ag@ZrO2@Ag　nanospheres　presented　remarkably　SERS　activity,　high　signal　reproducibility　(RSD　-　639%)　and　exceptional　storing　stability.　Subsequently,　the　Ag@ZrO2@Ag　nanospheres　acted　as　SERS　substrates　to　sense　Cr　(VI)　in　water　at　various　concentrations,　and　the　SERS　results　showed　great　linear　correlation　between　SERS　intensities　and　the　concentration　of　Cr　(VI)　(R　2　-　0.97)　with　the　detection　limit　of　0.5　JIM,　which　is　below　the　safety　level　(1　mu　M)　in　drinking　water　of　United　States　Environmental　Protection　Agency.　The　Ag@ZrO2@Ag　nanospheres　were　also　successfully　used　to　confirm　the　concentration　of　Cr　(VI)　in　real　industrial　wastewater.　These　results　demonstrated　the　extraordinary　potential　of　Ag@ZrO2@Ag　composite　nanospheres　serving　as　SERS　substrates　for　trace　and　quantitative　determination　of　Cr　(VI)　in　environmental　field.　(C)　2020　Elsevier　B.V.　All　rights　reserved.