Abstract: The effects of heat treatment parameters such as solution and aging temperature on the microstructures and tensile properties of in-situ 2vol%TiB/Ti-55531 composite forging stocks were studied, which were obtained by vacuum consumable arc melting and near-isothermal thermal-plastic deformation. The results show that, after 2vol%TiB/Ti-55531 composites and its matrix alloy solid heat treatment, the size and morphology of TiB enhanced phases change little after solid solution heat treatment, and the fine acicular α phase dispersed in the β phase matrix re-dissolve mostly, while the fine acicular α phase at grain boundary and local preferred orientation grow into the rod-like primary α phase, which result in the plasticity of materials increases and the strength decreases.After the solid-soluble state Ti-55531 matrix and its composite are subjected to timely heat treatment, the rod-like primary α phases are continuously coarsened, and the fine needle-like secondary α phases are precipitated, which obviously optimize the comprehensive mechanical properties of solution treatment composites and its matrix alloy. As the solution temperature increase from α+β to β region, the rod-like primary α phases disappear basically in the solution aging microstructure, and the number of fine needle-like secondary α phase increases obviously, resulting in the strength of materials increases and the plasticity decreases.With the increase of aging temperature, the rod-like primary α phases distribute along grain boundary in the microstructure of the composite and its matrix alloy have little change, while the fine needle-like secondary α phase distribute in the matrix of β phase coarsens, which reduces the strength of materials and increases its plasticity.