Abstract: The tensile properties and deformation mechanisms of a new precipitate-hardened Ni-Fe-base superalloy GH4650T are investigated after solutionizing and thermal aging at 750℃ for different hours. It is found that the strength increases firstly and decreases with time, whereas the tensile plasticity shows the opposite changing trend. After thermal aging for 48 h, the tensile strength is the best, whereas the elongation to fracture is the minimum at 5 h. Microstructural observations reveal that the grow kinetics of γ′ precipitates in the experimental alloy meet the Lifshitz-Slyozov-Wagner law, and the dominant deformation mechanism changes from particle shearing by weekly-coupled dislocations to by strongly-coupled dislocations and then to Orowan looping with increasing the γ′ precipitate size. Meanwhile, it is also found the fracture mechanism changes from transcrystalline fracture to intercrystalline fracture and then to ductile and brittle mixed fracture and the feature of ductile fractures becomes more and more obvious with precipitate size. Based on these observations, the relationship between the tensile properties and the operative deformation and fracture mechanisms is discussed.