Abstract: The influence of microstructure evolution on the tensile properties of the novel nickel-based powder metallurgy superalloys after long-term aging at 800 ℃ for 100~5000 h was studied. The results show that the grain size of the alloys does not change significantly with the increase of aging time, and the grain boundaries are coarsened and appear the discontinuous “sawtooth”. Secondary γ′ phase particles obviously coarsen which conforms to the LSW theory. The content of TCP phases precipitated increases with the increase of aging time. After aging for 1000 h, the intermittent long white precipitates are observed at the grain boundary. After aging for 2000 h, a large number of elongate needle-like precipitates appear in the grain. The content of TCP phases reaches the maximum after aging for 5000 h. Due to the coarsening of the secondary γ′ phase, the tensile strength and plasticity of the alloys at 700 ℃ gradually decrease with increasing the aging time. The tensile fracture has the characteristics of necking and dimple, and the fracture shows the dimple fracture.