Abstract: High strength TC21 and medium strength TC4-DT Ti-alloys with dissimilar damage tolerance were linear friction welded (LFW). Different heat treatments were selected for the joints. The microstructure and mechanical properties of the welded joints were studied after heat treatment. The results showed that good flash is formed on both side of the base metal after LFW. The surface of the flash is smooth and no defects are found at the root of the flash. The microstructure of the weld zone (WZ) is widmanstatten in as-welded condition. Precipitated acicular α phase is distributed in the weld zone after heat treatment. With heat treatment temperature increasing the precipitated α phases are coarsened. The impact properties and fracture toughness properties rises at the first and goes down latter with α coarsened. Tensile strength of the joints is equal to TC4-DT base metal. The high cycle fatigue limit of the joint is 558MPa at the temperature of 700℃ for 3 hours which is equal to TC4-DT base metal. Due to the fine microstructure of WZ the fatigue limit increases.