Tantalum (Ta) addition is one of the promising method for increasing the strength of Ni-based wrought alloys such as Inconel 718, because Ta is an element having a high melting temperature. For wrought alloys, it is necessary to make clear the phase relationships at 700~1000°C, but there is a few report on phase diagrams of Ni-Ta and Ni-Ta-Al systems at those temperatures. In this study, the phase diagram in Ni-rich region of Ni-Ta-Al system at 800°C, which is the important temperature for the practical use of the wrought alloys, was investigated. The equilibrium relations of each phase were examined by a conventional XRD, SEM/EDX and TEM observations. It was found that the γ-phase region expanded considerably towards Ta-rich compositional region in Ni-Ta-Al system at 800°C. Also, it was observed that the γ phase precipitated secondarily in the primary precipitated γ’ phase in Ni-10.5mol%Ta-5.5mol%Al alloy. Ni8Ta phase was not detected even in Ni-Ta binary system in this study, although this phase was reported previously.