The　effects　of　different　contents　of　Sc　addition　on　the　microstructures　and　properties　of　the　Al-4%Cu　alloy　were　studied　by　tensile　properties　measurement,　optical　microscope,　X-ray　diffraction　analysis,　scanning　electron　microscope　(SEM)　and　energy　spectrum　analysis.　The　experimental　results　show　that　rare-earth　element　Sc　is　capable　of　refining　the　dendritic　structure　of　the　Al-4%Cu　alloy,　the　tensile　strength　sigma(b)　and　yield　strength　sigma(0.2)　just　increase　a　little　when　the　content　of　Sc　is　lower　than　0.2%;　when　the　content　reaches　0.3%-0.4%,　sigma(b)　and　sigma(0.2)　slightly　decrease;　but　sigma(b)　and　sigma(0.2)　rise　again　when　the　Sc　content　is　0.5%,　though　both　of　them　are　lower　than　those　of　the　Al-4%Cu　alloy　without　Sc　addition.　However,　Sc　addition　has　little　influence　on　the　elongation　of　the　Al-4%Cu　alloy.　Adding　Sc　to　the　Al-4%Cu　alloy,　when　the　amount　of　Sc　is　lower　than　0.2%,　Sc　mostly　exists　in　the　alpha(Al)　solid　solution;　when　the　Sc　content　is　in　the　range　of　0.3%-0.5%,　only　a　part　of　Sc　exists　in　the　alpha-Al　solid　solution,　the　rest　appears　in　two　ways:　one　is　that　Sc　and　Al　form　Al3Sc　which　can　strengthen　the　alloy,　and　the　other,　Sc　interacts　with　Al　and　Cu　to　form　AlCuSc　phase.