The　precipitate　evolution　and　microstructure　stability　of　AlCuMgSiSc　alloys　with　Er　additions　were　intentionally　investigated.　It　reveals　that　the　Cu-containing　metastable　precipitates　(rod-liked　Q　＇　and　lath-liked　L　precipitates)　are　promoted　and　achieved　highest　tensile　strength　of　similar　to　441.3　MPa　through　precipitation　strengthening　after　aging　at　12　h　in　AlCuMgSiErSc　alloy.　Meanwhile,　the　AlCuMgSiErSc　alloy　shows　approximately　similar　to　6.9　%　and　similar　to　10.8　%　higher　UTS　(27.7　MPa)　and　YS　(34.1　MPa)　than　AlCuMgSiSc　alloy　after　severe　over　aging　for　150　h,　respectively.　Surprisingly,　the　sigma-Al5Cu6Mg2　precipitates　are　rarely　observed　in　AlCuMgSiErSc　alloy　indicating　that　the　formation　of　sigma-Al5Cu6Mg2　is　inhibited.　The　excellent　thermal　stability　can　be　explained　by　the　high　density　of　Q　＇　precipitates　with　hybrid　structures　and　L　precipitates.　Moreover,　Er　solute　atoms　preferentially　segregate　at　the　interface　of　the　Q　＇　precipitates　and　enrich　the　0＇　precipitate,　which　inhibits　the　diffusion　of　solute　atoms　and　stabilizes　the　coarsening　of　precipitates.　This　work　may　provide　a　strategy　for　designing　Al-Cu　series　alloys　with　thermally　stable　microstructures.