Abstract: Electron beam welding was carried out on 56 mm-thick Ti80 titanium alloy, and the microstructure and mechanical properties of the welded joint were investigated. The results show that microstructure of weld metal is composed of martensite α phase and β phase. The boundary of the fusion zone is clear, and the overheated zone is narrow. The microstructure of HAZ consists of primary α phase, martensite α phase and β phase. Micro-hardness of the Ti80 joint decreases from weld zone to base metal. The joint has excellent mechanical properties, and its tensile strength is up to 935. 3 MPa, higher than that of the base metal. Impact energy increases from the weld zone to the base metal and ductilility features the fracture of the joint. The bending tests show no flaw has appeared in the specimens bended.