The　evolution　of　mechanical　properties　and　microstructure　of　Al-4.　5Mg-0.　7Mn-0.4Er-0.　1Zr　alloy　after　annealing　at　different　temperatures　was　studied　by　means　of　tensile　test,　OM,　SEM　and　TEM　observations.　The　results　show　that　annealing　temperature　has　a　significant　affect　on　mechanical　properties　and　microstructure　of　the　experimental　alloy.　After　annealed　below　200　°C　for　1　h,there　is　little　change　of　mechanical　properties　of　the　alloy　so　it　happens　only　with　recovery;　and　annealed　at　200-300　°C　for　1　h,　the　recrystallization　happens　now,　and　mechanical　properties　of　the　alloy　change　remarkably.　After　annealed　over　300　°C　for　1　h,　the　alloy　grains　coarsen,　but　there　is　a　little　change　for　mechanical　properties.　The　phase　particles　containing　Er　remarkably　inhibit　the　coarsening　of　recrystallized　grains.