The isothermal section of Ag-Cu-Er ternary phase diagram at 923 K containing 0~33.3 at % Er has been determined by XRD,SEM and EPMA.In order to confirm the phase constituents,the XRD profile of Cu9Er2 has been firstly measured in this work due to the lack of this data in the literatures.In addition,five three-phase regions and two tie-lines have been found in the isothermal section.With the aid of the EPMA analysis,the solubilities of the third component in the binary compounds of Ag51Er14,Ag2Er,Cu9Er2 and Cu2Er have been identified.No ternary intermetallic compound has been found.