Samples　of　Al-Mg-Mn-Zr-Er　alloys　were　welded　by　the　method　of　TIG　welding.　Microstructures　of　base　metal　and　welded　zones　were　analyzed　by　optical　microscopy　(OM),　electron　probe　micro-analyzer　(EPMA)　and　transmission　electron　microscopy　(TEM).　Particular　emphasis　was　laid　on　the　existence　form　of　Er　and　its　effect　on　the　microstructure　and　the　phase　composition　of　the　fusion　zone.　Results　reveal　that　the　trace　rare　earth　element　Er　mainly　exists　in　the　form　of　primary　and　secondary　Al3Er　phase,　which　play　significant　roles　of　refining　and　strengthening　the　fusion　zone.　A　characteristic　Equiaxed　Zone　(EQZ)　is　obtained　beside　the　fusion　boundary　between　the　partially　melted　zone　and　the　fusion　zone　(FZ)　due　to　the　addition　of　Er.