An isothermal section of the Co–Ni–Nb system at 1123K was experimentally determined using the diffusion triple technique together with electron probe micro-analysis. Two binary compounds, Ni6Nb7 and Co7Nb6 formed a continuous solid solution (Ni,Co)6Nb7 in the ternary. Ni could partially substitute Co in Co2Nb and Nb in Co3Nb. The Co could partially replace Ni in Ni3Nb. One ternary phase, named “X”, was observed with an homogeneity range covering 20 to 68at%Co and 23 to 26at%Nb. Furthermore, 5 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) were determined in this isothermal section.The Isothermal Section of the Co–Ni–Nb Ternary System at 1123K Determined by Diffusion Triple Technique. Y.M.Wang, H.S.Liu, F.Zheng, Z.P.Jin: Journal of Alloys and Compounds, 2008, 454[1-2], 501-5