Phase diagrams of two isothermal sections of the Ni-Ti-Ta ternary system at 1000 and 1200 °C in a full composition range were determined by X-ray diffraction and electron probe microanalysis. The experimental results indicated a ternary compound τ phase with low solid solubility and composition ranges of (16.3-22.4) at.% Ta, (15.9-24.1) at.% Ti and (58.5-60.0) at.% Ni at 1000 °C. The two terminal solid solutions (bcc-(Ta) and β-Ti) formed a continuous solid solution at 1000 and 1200 °C. A certain amount of Ti can dissolve into Ni-Ta intermetallic compounds near the Ni-Ta side, with the highest value of 21.9 at.% observed in the Ni₂Ta compound at 1000 °C.