The isothermal section of the Nb-Y-Si ternary system at 873 K was investigated over the whole concentration range mainly by powder X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy dispersive analysis （EDX）. This isothermal section con- sisted of 10 single-phase regions, 17 two-phase regions, and 8 three-phase regions. The existence of the binary compounds, i.e., Y5Si3, Y5Si4, YSi, Y3Sis, YSi〉 NbsSi3 and NbSi2 at 873 K was confirmed. On the basis of XRD patterns, the structure types of Y3Si4, Y3Si5 and YSi2 were discussed. No ternary compound and no detectable solid solubility in the binary compounds were found.
