Al-6Zn-2Mg　and　Al-6Zn-2Mg-0.4Er　alloys　were　prepared　by　cast　metallurgy.　The　effects　of　trace　Er　on　the　mechanical　properties,　recrystallization　behavior　and　age-hardening　characteristic　of　Al-Zn-Mg　alloy　were　studied.　The　effect　of　Er　on　microstructures　was　also　studied　by　OM,　XRD,　SEM,　EDS　and　TEM.　The　results　show　that　the　addition　of　Er　on　Al-6Zn-2Mg　alloy　is　capable　of　refining　grains　obviously.　The　addition　of　Er　can　improve　the　strength　considerably　by　strengthening　mechanisms　of　precipitation　and　grain　refinement.　With　the　addition　of　Er　into　Al-6Zn-2Mg　alloy,　the　aging　process　is　quickened　and　the　age-hardening　effect　is　heightened.　Er　additive　can　retard　the　recrystallizing　behavior　of　Al-6Zn-2Mg　alloy　and　cause　the　increase　of　recrystallization　temperature　due　to　the　pinning　effect　of　fine　dispersed　AbEr　precipitates　on　dislocations　and　subgrain　boundaries.