High-density of arrays of self-oriented boron nanowires grown on silicon substrates were synthesized by radio-frequency magnetron sputtering with a target of highly pure boron and boron oxide mixture using argon as the sputtering atmosphere. TEM studies show that the conventional growth mechanisms such as Frank screw-dislocation mechanism and the vapor-liquid-solid mechanisms are not suitable for the one-dimensional growth of boron nanowires. The oxide-assisted cluster-solid mechanism for the Si and Ge crystalline nanowires is not completely suitable for our case. The vapor-cluster-solid mechanism is proposed for the well-aligned growth of the amorphous boron nanowires. (C) 2002 Elsevier Science B.V. All rights reserved.