The　effect　of　adding　small　amounts　of　rare　earth　Er　on　the　microstructure　of　an　Al-Cu-Si　braze　alloy　has　been　investigated.　Several　Al-20Cu-7Si　braze　alloys　containing　various　contents　of　Er　were　prepared,　and　their　melting　temperature,　microstructure,　hardness,　and　wettability　in　contact　with　3003　aluminum　alloy　substrates　were　determined.　The　results　indicate　that　the　constituents　of　the　microstructure　of　Al-20Cu-7Si-Er　braze　alloys　are　similar　to　those　in　the　Al-20Cu-7Si　alloy,　and　comprise　of　solid　solutions　of　aluminum,　silicon,　and　the　intermetallic　compound　CuAl2.　When　the　Er　content　increases,　the　size　of　the　Al　phase　decreases,　and　the　needle-like　Si　phase　is　thickened,　and　transformed　to　a　blocky　shape.　Moreover,　small　amounts　of　Er　can　improve　the　wettability　and　hardness　of　the　Al-20Cu-7Si　braze　alloy;　however,　the　melting　temperature　of　the　Al-20Cu-7Si　alloy　does　not　change.