[en] An isothermal section of the Co-Ni-Nb system at 1123 K was experimentally determined using diffusion triple technique together with electron probe microanalysis (EPMA). Two binary compounds, Ni₆Nb₇ and Co₇Nb₆ form a continuous solid solution (Ni,Co)₆Nb₇ in the ternary. Ni can partially substitute Co in Co₂Nb and Nb in Co₃Nb. Co can partially substitute Ni in Ni₃Nb. One ternary phase named as 'X' has been observed with homogeneity range covering 20-68 at.% Co and 23-26 at.% Nb. Furthermore, five three-phase equilibria, Co₃Nb + Co₂Nb + X, X + (Ni,Co)₆Nb₇ + Co₂Nb, X + Co₃Nb + γ(Co,Ni), Ni₃Nb + X + (Ni,Co)₆Nb₇ and Ni₃Nb + X + γ(Co,Ni) have been determined in this isothermal section