Fracture　toughness　test　on　Ti　alloy　BT20　and　laser-welded　joints　was　carried　out.　Meanwhile,　hardness　distribution　and　microstructure　of　the　alloy　and　welded　joints　were　investigated.　Fracture　test　indicated　that　brittle　unstable　fracture　occurred　after　ductile　crack　initiation　and　slow　propagation　for　all　the　compact　tension　(CT)　specimens,　except　one　welded　joint　specimen　was　brittle　crack　initiation.　Fracture　toughness　of　base　metal　was　obviously　higher　than　that　of　welded　joint,　and　rolling　directions　had　no　obvious　effect　on　fracture　toughness　of　base　metal.　Fracture　toughness　of　heat-affected　zone　(HAZ)　was　between　the　base　metal　and　weld　metal.　Postweld　heat　treatment　not　only　not　improved　the　fracture　toughness　of　welded　joint,　but　also　had　the　trend　of　deterioration.　Addition　of　activating　agent　had　no　obvious　effect　on　fracture　toughness　of　weld　metal,　but　it　improved　the　length　of　ductile　crack　propagation.