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The thermal annealing conditions in nitrogen ambient for the self-synthesis of tungsten carbide nanowires from sputter-deposited WC(x) films were investigated. Experimental results show that the temperature window for the growth of nanowires lies in the range of 500-750 °C with the corresponding annealing time interval ranging from 2.5 to 0.25 h. The diameter, length, and density of the grown nanowires are in the range of 10-15 nm, 0.1-0.3 µm, and 210-410 µm(-2), respectively. The degree of carbon depletion in the annealed WC(x) films plays a crucial role in determining both the shape and density of the self-synthesized nanowires. Nanowires synthesized at lower temperatures were seen to be smaller in dimension but higher in density. Material analysis reveals that the phase transition from WC to W(2)C arising from decarburization of the WC(x) film during thermal annealing should be responsible for the self-synthesis of nanowires.