A　kind　of　needle-like　sandwich-combined　precipitation　product　(denoted　as　η)　was　found　to　be　formed　concurrently　with　the　equilibrium　β-phase　in　a　Mg-Gd-Y　alloy　subjected　to　duplex　aging　at　200　°C　and　250　°C,　respectively,　and　its　structure　was　characterized　by　high-angle　annular　dark-field　scanning　transmission　electron　microscopy　(HAADF-STEM)　technique.　It　had　been　clearly　revealed　that　the　η-precipitate　consists　of　a　new　base-centered　orthogonal　(BCO)　precipitate　as　a　long　core　(B)　which　is　invariably　sandwiched　by　the　face-centered　cubic　(FCC)　Gd(Y)　solute　precipitate　platelets　(F)　as　surface-shells.　The　orientation　relationships　involved　with　the　unique　F-B-F　sandwiched　precipitation　for　the　η　constructing　in　the　Mg　matrix　were　determined　to　be　F//,B,{010}F//{010}B　and　F//Mg,{010}F//{101¯0}Mg,　respectively.　©　2020　Elsevier　B.V.