Effect　of　trace　rare　earth　Er　addition　on　the　aging　behavior　of　1420　alloys　was　studied　using　hardness　testing.　Precipitation　behavior　during　aging　was　investigated　by　electron　microscopy　transmission.　It　is　found　that　small　amounts　of　Er　can　modify　the　aging　behavior　of　1420　alloy,　for　example,　improve　the　hardness　and　shift　peak　aging　time.　All　those　results　may　be　attributed　to　the　increase　of　diffusion　coefficient　of　L　atom　in　the　Al　matrix　added　with　Er.　As　a　consequence,　rate　of　nucleation　and　growth　of　delta＇　(Al3Li)　was　promoted;　the　Al3Er　particles　act　as　preferential　sites　for　the　nucleation　and　growth　of　delta＇,　which　in　turn　results　in　the　presentation　of　more　composite　particles.