The microstructure and mechanical properties of linear friction welded Ti-22Al-25Nb alloy were studied after aging at 840 ℃ for 2 h. The results show that the welded joint can be divided into three parts: weld zone, TMAZ and base metal. The microstructure of weld zone is dominated by B2 phase, while the volume fraction of α2 and O phase is relatively small. Only a small amount of α2 and O phase transformed into B2 phase in TMAZ, and the morphology of α2 phase changes little. The EBSD results show that the crystallographic orientation in base metal cannot be inherited into the final weld structure. After aging at 840 ℃, the recrystallization and the precipitation of O phase can be observed in weld zone. The decomposition of α2 phase is insufficient in TMAZ, while the rim-O phase precipitated around α2 phase can be observed. In base metal, the O phase has grown up, while the α2 phase has no obvious change. After the heat treatment, the strengthening of the O phase precipitation and the refined grains significantly increased the mechanical properties of the joint.