The　aging　behavior　of　dilute　Al-Er-Zr　alloy　and　the　coarsening　behavior　of　Al3(Er1-xZrx)　precipitate　were　investigated　by　micro-hardness　measurements,　transmission　electron　microscopy　and　high　resolution　electron　microscopy.　The　results　show　that　the　maximum　hardness　of　Al-0.04Er　is　40.3HV,　which　is　obtained　after　aging　at　375°C　for　5　min,　and　the　hardness　decreases　quickly　with　overaging.　Overaging　is　delayed　in　Al-Er-Zr　compared　with　the　Zr-free　alloy,　which　indicates　that　the　addition　of　Zr　improves　the　thermal　stability　of　Al-Er　alloy.　In　ternary　alloy　Al-Er-Zr,　the　hardness　has　a　second　peak　as　synergetic　precipitation　of　Er　and　Zr;　the　second　is　53.5HV,　which　is　significantly　higher　than　the　peak　hardness　of　Al-Er　binary　alloy.　The　Al3(Er1-xZrx)　precipitate　coarsens　gradually　at　higher　temperature.　The　average　precipitation　diameter　(d)　increases　with　aging　time　t　as　a　function　shown　in　LSW　theory.