BNC nanotubes were prepared by a high-energy ball milling and annealing method. Graphite carbon (C) and hexagonal boron nitride (h-BN) powder was first milled at room temperature to generate highly disordered nanoporous particles with a metastable structure. Upon elevated temperature annealing up to 1300 °C, these nanoporous particles were chemically and thermally activated to grow BNC nanotubes with both cylindrical and bamboo-like morphology. The cylindrical tubes have smaller diameters from 40 to 60 nm and lengths up to 2 μm. The bamboo tubes have larger diameters from 80 to 150 nm and lengths up to 10 μm. The formation mechanisms of different nanostructures are discussed.