In　the　present　work,　the　effect　of　a　small　amount　of　rare　earth　Er　addition　on　the　microstructure　of　Al-Cu-Si　brazing　alloy　has　been　investigated.　In　the　study,　the　Al-20Cu-7Si　brazing　alloys　with　various　Er　contents　were　prepared.　3003　aluminum　alloy　was　chosen　as　a　substrate.　The　microstructure　of　the　brazed　alloys　was　carefully　observed.　In　addition,　melting　temperature,　wettability　and　hardness　of　the　brazing　alloys　were　measured.　The　results　indicate　that　the　constituent　of　the　microstructure　of　Al-20Cu-7Si-Er　brazed　alloy　is　similar　to　the　Al-20Cu-7Si,　which　is　mainly　comprised　of　solid　solutions　of　aluminum,　silicon　and　the　intermetallic　compounds　CuAl2.　When　the　Er　content　increases,　the　size　of　Al　phases　is　decreased,　and　the　filament-like　or　needle-like　Si　phase　is　thickened.　The　Si　phases　dominating　in　the　shape　of　a　filament　or　needle　are　transformed　to　those　in　the　shape　of　a　block　when　Er　content　is　increased.　Moreover,　adding　a　small　amount　of　Er　can　improve　the　wettability　and　hardness　of　the　Al-20Cu-7Si　brazing　alloy.　However,　the　melting　temperature　of　the　Al-20Cu-7Si　alloy　is　almost　unchanged　when　a　small　amount　of　Er　is　added.　©　Higher　Education　Press　and　Springer-Verlag　GmbH　2008.