In　order　to　improve　the　mechanical　properties　of　Al-Si　alloys　fabricated　by　selective　laser　melting　process,　the　microstructure　and　mechanical　properties　of　Er/Zr　modified　A357　(Al-7Si-0.6　Mg)　alloy　in　as-built　and　stress　relief　annealing　conditions　were　studied.　The　results　show　that　adding　0.15　wt.%　Er　helps　to　refine　the　cellular　size,　which　is　formed　by　eutectic　Si　network.　The　(Al,Si)3(Er,Zr)　phases　were　precipitated　during　the　solidification　of　Er-Zr　composite　modified　sample,　which　could　act　as　inoculants　to　promote　the　formation　of　equiaxed　grains　and　refine　the　grain　size.　The　average　grain　size　of　0.8Er-0.4Zr　sample　was　only　3.1　±　1.4　µm.　The　yield　strength,　tensile　strength　and　elongation　reached　333　±　2　MPa,　454　±　1　MPa　and　12.5　±　1%,　respectively.　After　stress　relief　annealing,　eutectic　Si　was　spheroidized　and　its　size　was　increased,　resulting　in　a　decrease　of　strength　and　an　increase　of　elongation.　At　the　same　time,　the　nano-sized　L12-structure　particles　were　precipitated　in　the　Er-Zr　composite　modified　sample,　which　would　make　up　for　the　loss　of　strength　and　level　it　up　to　a　certain　extent.　Therefore,　Er-Zr　composite　modification　could　be　an　effective　method　to　improve　the　comprehensive　mechanical　properties　of　SLM　processed　Al-Si　alloys.　　©　2022　The　Author(s).