[en] Highlights: • The homogeneity range of β (Ti,Nb) phase were identified using one diffusion couple. • Solid solubility of 9 binary intermetallic compounds were confirmed. • Nine three-phase fields were detected using EPMA and XRD. • Phase equilibria of Ti-Nb-Co at 1000 °C in whole composition range established The phase relations in the Ti-Nb-Co system are of great importance for the design of high temperature Ti alloys. The isothermal section of Ti-Nb-Co system at 1000 °C has been established using one diffusion couple supplemented with 13 key alloys. Phase relations and ternary solubility of the binary compounds were determined using electron probe microscopy (EPMA), wave dispersive X-ray spectrometer (WDS) and X-ray diffraction (XRD) techniques. There are 19 two-phase equilibria and 9 three-phase equilibria in the isothermal section at 1000 °C. The determined maximum solubility of Nb in TiCo₃, TiCo₂ (h), TiCo₂ (c), TiCo, Ti₂Co were 6.22, 17.21, 2.29, 22.88 and 2.49 at.%, respectively. Nb₂Co₇, NbCo₃, NbCo₂, Nb₆Co₇ dissolves up about 0.33, 17.75, 13.26 and 10.81 at.% Ti, respectively. All of the binary phases have a certain composition range at 1000 °C except Nb₂Co₇. The phase diagram of Ti-Nb-Co system varied greatly when the temperature raised from 900 °C to 950 °C, but the changes was not so big when temperature increased from 950 °C to 1000 °C.