Abstract The microstructural features and age-hardening behaviors of spray formed Ni-based superalloy have been investigated. The alloy was solutioned at 1140 °C for 8 h followed by ageing at 780 °C for various time in the range of 2 h to 12 h. The microhardness, γ ′ precipitates size, morphology, electrical conductivity and positron annihilation lifetime as a function of ageing time were measured. The results show that the microhardness reaches a maximum after ageing for 8 h; at that time, the γ ′ precipitates grow up to a critical size of 56 nm. However, when the size of γ ′ precipitates is beyond the critical size, the microhardness decreases. The electrical conductivity rapidly increases up to its maximum value of 32%IACS with further increase of ageing time of 6 h, but the positron annihilation lifetime drops down to its minimum of 149 ps at this moment, and a maximum of 297 ps is reached after ageing for 10 h. The results are attributed to the changes of defect concentration and γ ′ precipitates size evolution during the ageing process.