A high quantity and yield (up to 85%) of boron nitride (BN) nanotubes have been produced using a mechanothermal method. Elemental boron powders were first mechanically milled at room temperature in NH₃ atmosphere and subsequently heated in N₂ gas at 1200 °C for up to 16 h. The BN nanotubes obtained have either multiwalled cylindrical or bamboolike structures, suggesting different growth processes. The high formation yield of BN nanotubes is due to a high density of nanostructured nuclei created by an extensive milling treatment.