The　microstructure　and　mechanical　properties　of　the　Mg-5Y-4Gd-0.5Zn-0.4Zr　alloy　have　been　investigated.　The　results　suggested　that　the　14H　long　periodic　stacking　ordered　(LPSO)　structure　was　formed　during　isothermal　homogenization.　Furthermore,　the　presence　of　the　14H　LPSO　structure　resulted　in　refined　microstructure　and　weak　texture　while　harmful　to　improve　ageing　hardening　response　after　hot　extrusion.　The　Mg-5Y-4Gd-0.5Zn-0.4Zr　alloy　after　homogenization　for　16　h　at　500　degrees　C　(as-extruded　alloy　B)　followed　by　subsequent　hot　extrusion　displayed　the　highest　peak　hardness　value　during　ageing　at　220　degrees　C.　The　yield　tensile　strength　and　the　ultimate　tensile　strength　of　the　peak-aged　alloy　B　were　about　300　MPa　and　370　MPa,　respectively.　(C)　2013　Elsevier　Ltd.　All　rights　reserved.