In order to develop new Co-base superalloys and understand the relationships between microstructures and properties in the Co-V-Ta ternary system, four isothermal sections of the Co-V-Ta ternary system at 1300, 1200, 1100 and 900 ℃ are experimentally established.Importantly, the alloys with γ/γmicrostructure are obtained.The present results show that: (1)the C14 single phase region is formed at 1100 and 900 ℃, while the C36 phase forms a single region at 900 ℃;(2) the analogous occupation behaviors of V and Co atoms, substituting for each other, can be indicated in C14, C15 and C36 Laves-phases;(3) the solubility of Ta in σ-Co2V3 phase slightly increases with increasing temperature;(4) Co-V-Ta base alloys fabricated show the attractive mechanical properties.The experimental data obtained in the present work is not only essential for the thermodynamic assessment of the Co-V-Ta ternary system, but also important for the development of the Co-base alloys.