A boron nitride (BN) nanostructure, conical BN nanorod, has been synthesized in a large quantity on Si substrates for the first time via the ball-milling and annealing method. Nitridation of milled boron carbide (B4C) powders was performed in nitrogen gas at 1300 degrees C on the surface of the substrates to form the BN nanorods. The highly crystallized nanorods consist of conical BN basal layers stacked along the nanorod axis. Ball milling of the B4C powders can significantly enhance the nitridation of the powders and thus facilitate the formation of nanorods during the annealing process.