Boron nitride (BN) nanotubes of different sizes and tubular structures exhibit very different mechanical and chemical properties, as well as different applications. BN nanotubes of different sizes and nanostructures have been produced in different nitriding gases in a milling and annealing process, in which elemental boron powder was first milled in NH3 for 150 h and subsequently annealed at 1,200 degrees C for 6 h. The influence of nitriding gases was investigated by using N-2, NH3, N-2-H-2 mixture gases. A relatively slow nitriding reaction in NH3 gas leaded to a 2D growth of BN (002) basal planes and the formation of thin BN nanotubes without the help of metal catalysts. Fast nitriding reactions occurred in N-2 or N-2-H-2 mixture gases, catalyzed by metal particles, resulted in 3D crystal growth and the formation of many large cylindrical and bamboo tubes.