Abstract: The relationship between tensile ductility and microstructure of the weld of TB2 titanium sheet alloy has been studied.Tensile test,bending test,and hardness test of specimens with and without heat-treatment after automatic TIG welding have been conducted at ambient temperature.The microstructures andfractured surfaces have been studied by optic microscopy,electron microscopy(replica and thin foil) and scanning electron microscopy.It has been found that the tensile ductility of the weld of TB2 titanium alloy depends on the morphology,quantity and size of the α-phase.The rate of ageing in the weld is higher than that in the base metal.The tensile ductility of the weld after 2-stage ageing has been raised considerably due to the blunting of the tips of α-phase precipitates.The presence of precipitation-free zone near grain boundaries is responsible for the intercrystalline fracture.The presence of continuous α-phase precipitation along grain boundaries embrittles the alloy substantially.