Magnesium　rare-earth　(Mg-RE)　alloys　have　great　potential　in　lightweight　applications　because　of　the　high　specific　strength.　Wire-arc　directed　energy　deposition　(WA-DED)　exhibits　great　prospects　for　the　fabrication　of　largescale　monolithic　structural　components　with　high　manufacturing　flexibility.　In　this　work,　a　single-pass　multilayer　Mg-10Gd-3Y-1Zn-0.5Zr　(wt%,　GWZ1031K)　deposit　was　prepared　via　WA-DED.　Electron　backscatter　diffraction　(EBSD),　scanning　electron　microscopy　(SEM),　and　transmission　electron　microscopy　(TEM)　are　conducted　to　systematically　explore　the　microstructural　evolution　during　the　WA-DED　process　and　the　subsequent　heat　treatment.　The　GWZ1031K　alloy　deposit　fabricated　by　WA-DED　exhibits　uniform　equiaxed　grain　structure　whose　average　grain　size　is　22.3　+/-　5.6　mu　m.　The　(Mg,Zn)(3)(Gd,Y)　phase　and　RE　segregation　can　be　observed　along　the　alpha-Mg　grain　boundaries　(GBs).　A　number　of　needle-like　gamma＇/gamma　＇＇　phases　embedded　in　the　alpha-Mg　grain　interior　(GI).　In　addition,　there　is　a　small　number　of　fine　RE-rich　cubic　phase　and　(Gd,Y)(2)O-3　particles.　The　deposit　shows　significantly　enhanced　ductility　and　slightly　improved　strength　after　solution　treated　at　500　degrees　C　for　12　h.　After　the　solution　treatment,　the　intergranular　(Mg,Zn)(3)(Gd,Y)　eutectics　dissolve　into　the　matrix　and　long　period　stacking　ordered　(LPSO)　phases　precipitate　from　the　GBs　into　the　GI,　contributing　to　the　enhancement　in　ductility.　Besides,　the　LPSO　phase　along　with　the　existing　RE-rich　cubic　phase,　(Gd,Y)(2)O-3　and　Zr　particles　at　GBs　also　play　a　role　in　hindering　grain　growth.　The　high-density　nanoscale　beta＇　phases　appear　in　the　GI　after　aging　treated　at　200　degrees　C　for　24　h,　resulting　in　the　remarkable　precipitation　strengthening.　In　comparison　with　the　solution-treated　GWZ1031K　deposit,　the　aging-treated　exhibits　a　prominently　improved　ultimate　tensile　strength　of　337　+/-　7　MPa　in　the　building　direction　(BD)　and　331　+/-　5　MPa　in　the　travelling　direction　(TD).　It　is　envisaged　that　the　WADED　manufacturing　method　will　provide　a　simple　and　effective　route　to　fabricate　large-scale　Mg-RE　alloy　components　for　various　applications.