Er　and　Zr　modified　Al-Mg　alloy　was　manufactured　by　selective　laser　melting.　The　effect　of　aging　treatment　on　phase　evolution　and　mechanical　properties　of　alloy　has　been　studied.　The　results　show　that　bimodal　grain　structures　(2.8　+/-　1.1　mu　m)　could　be　obtained,　thanks　to　the　Al3Zr　primary　phases　promoting　the　formation　of　equiaxed　grains　(0.8　+/-　0.3　mu　m)　at　the　boundary　of　molten　pool.　During　the　aging　of　375　degrees　C,　Al3(Er,Zr)　particles　with　the　size　of　2-5　nm　were　produced　via　synergistic　precipitation　of　Er　and　Zr,　which　would　greatly　improve　the　strength　and　reach　510　+/-　9　MPa.　At　the　same　time,　the　Mg-rich　phase　was　dissolved,　the　Mn-rich　phase　was　precipitated,　and　dislocations　could　accelerate　the　diffusion　of　solute　atoms　during　the　evolution　of　the　phases.