Fracture　toughness　of　a　damage　tolerant　Ti6Al4V　(TC4-DT)　alloy　and　its　electron　beam　welded　joint　was　investigated　using　compact　tension　specimens.　Moreover,　tensile　test,　microhardness　test　and　microstructure　examination　were　carried　out.　The　result　indicates　that　the　weld　metal　is　strength　overmatching.　The　tensile　strength　and　microhardness　of　the　weld　metal　are　higher　than　those　of　the　base　metal,　but　the　ductility　and　the　energy　absorbed　before　fracture　are　lower.　In　addition,　the　fracture　toughness　K-1c　of　the　base　metal　is　relatively　high.　The　fracture　toughness　of　the　weld　metal　decreases　compared　with　the　base　metal.　It　is　expected　that　the　toughness　reduction　of　the　weld　metal　is　mainly　related　to　the　as　solidified　coarse　beta　columnar　grain　structure　containing　martensite　in　comparison　with　the　bimodal　structure　of　the　base　metal.　Moreover,　fractographic　observation　shows　that　the　fracture　mode　of　both　weld　and　base　metals　is　found　to　be　ductile.