The　present　work　focuses　on　the　effects　of　rare　earth　(RE　=　Gd　and　Er)　contents　on　the　microstructural　evolution　and　mechanical　performance　of　Mg-Gd-Er-Zr　alloys.　Three　different　alloys,　i.e.,　Mg-12Gd-2Er-0.4Zr,　Mg-14Gd-1Er-0.4Zr,　and　Mg-14Gd-2Er-0.4Zr,　are　fabricated　and　subjected　to　double-pass　extrusion.　Incomplete　dynamic　recrystallization　(DRX)　resulted　in　a　non-homogeneous　grain　structure　with　coarse　and　refined　equiaxed　grains　during　single-pass　extrusion.　In　contrast,　the　grain　size　decreased　dramatically　after　double-pass　extrusion,　and　a　high　number　of　fine　Mg5RE　particles　precipitated　in　the　Mg-14Gd-2Er-0.4Zr　alloy　than　the　other　two　extruded　alloys.　Moreover,　the　Mg5RE　particles　larger　than　1　mu　m　contributed　to　increase　the　DRX　fraction,　whereas　the　finer　ones　exerted　a　strong　pinning　effect　on　grain　boundaries.　The　volume　fraction　of　beta＇　precipitates　increased　with　increasing　RE　content　in　the　matrix.　A　large　volume　fraction　of　beta＇　precipitates　in　the　alloy　will　primarily　result　in　higher　hardness　and　strength　in　the　peak-aged　condition.　After　peak-aging　treatment,　the　double-pass　extruded　Mg-14Gd-2Er-0.4Zr　alloy　exhibited　a　good　yield　strength　of　481　+/-　3.7　MPa　and　an　adequate　elongation　of　3.2　+/-　0.6%.　The　influence　mechanisms　of　grain　refinement,　fine　particles,　and　the　strengthening　of　beta＇　precipitates　are　discussed.