The　Al-7Si-0.3　Mg　(A356)　alloys　with　various　contents　of　the　rare　earth　element　Er,　Zr　were　prepared　by　the　conventional　casting　technique.　The　effect　of　Er,　Zr　composite　modifications　on　the　microstructure　and　mechanical　properties　of　A356　alloys　was　investigated　using　the　optical　microscopy　(OM),　scanning　electronic　microscopy　(SEM),　energy　spectrum　analysis　and　mechanical　testing.　The　results　show　that　addition　of　0.3　wt%　Er　and　Zr　had　an　excellent　refining　effect　on　alpha-Al　grains　and　a　modification　effect　on　Si　containing　phase　in　the　as-cast　state.　The　size　of　alpha-Al　dendrite　reduced,　the　acicular　eutectic　Si　became　short　rod-shaped　or　granular.　When　Er　and　Zr　content　was　0.3　wt%,　the　tensile　strength　and　hardness　of　the　alloys　reached　up　to　maximum　values.