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A grain morphology index f1 characteristic of the configuration of secondaryrecrystallized grains grown in tungsten wires is derived after making their contours clear inthree dimensions. Tensile and hardness tests are made using the wires with different grainmorphologies at room temperature. It is then investigated through f1 how the grainmorphology is connected to brittleness of doped wires. The fracture modes are classified tobe ductile and brittle at each of the two regions, which are separated so that each of them isbelow and above a certain value of f1 respectively. The morphological features of grains toprevent fatal brittleness of wires are demonstrated.