Abstract: Solid solution aging treatment was performed on Ti-0.3Mo-0.8Ni titanium alloy, and then the microstructure and mechanical properties of the treated Ti-0.3Mo-0.8Ni alloy were studied through the optical microscope imaging, room temperature tensile test, and scanning electron microscopy characterization. The results show that the content of primary α phase decreased and even disappeared with the increase of solution temperature, and meanwhile, a large amount of secondary α phase precipitated. The microstructure type of the alloy gradually changed from the bimodal structure to the fine lamellar structure. The plasticity of the alloy decreases gradually with the increase of solution temperature, while the strength shows the opposite trend with plasticity. When the solid solution temperature is in the two-phase region, there are a large number of ductile dimples, and a small number of secondary cracks and voids on the tensile fracture surface. When the solid solution temperature is in the single-phase region, the tensile fracture has the crystalline morphology with cleavage steps and tearing edges, and a small number of tiny dimples are distributed on the fracture surface.