Investigation　of　fracture　toughness　on　Ti-6.5Al-2Zr-1Mo-1V　alloy　thin　sheet　and　its　laser-welded　joints　has　been　carried　out.　In　the　test　compact　tension　(CT)　specimens　and　single　specimen　technology　were　used.　In　addition,　hardness　distribution　and　microstructure　of　the　welded　joints　were　examined.　Fracture　test　indicates　that　brittle　unstable　fracture　occurs　after　slow　crack　propagation　for　all　the　specimens,　except　that　one　heat　affected　zone　(HAZ)　specimen　is　brittle　crack　initiation.　It　is　found　that　rolling　directions　have　no　obvious　effect　on　fracture　toughness　of　base　metal.　Moreover,　fracture　toughness　of　weld　metal　is　obviously　decreased　in　comparison　with　base　metal　whatever　in　as-welded　condition　or　in　stress　relief　condition.　Post-weld　heat　treatment　(PWHT)　leads　to　fracture　toughness　of　the　welds　further　decreasing.　Fractography　observation　shows　that　the　fracture　mode　is　predominantly　dimpled　in　base　metal.　However,　there　exists　intergranular　fracture　in　the　weld　metal.　Thus,　the　transition　of　fracture　mode　from　both　base　metal　and　HAZ　to　weld　metal　may　lead　to　dramatic　decrease　in　fracture　toughness.　Microstructure　examination　reveals　that　the　microstructure　of　weld　metal　consists　of　large　grains　with　fine　acicular　structure.　The　formation　of　fine　alpha　acicular　structure　is　due　to　rapid　cooling　during　laser　welding.　After　PWHT,　the　acicular　structure　is　coarsened.