Well-aligned amorphous boron nanowires are prepared using magnetron sputtering. One type is straight without any branch and the other type is feather-like in morphology. Electron energy-loss spectroscopy has been used to detect the existence of oxygen in these boron nanowires. A Gatan imaging filter system, which is attached to a Philips CM200-field emission gun transmission electron microscope, has been used to acquire elemental mapping of boron and oxygen using inner-shell ionization edges. It is revealed that both the straight and feather-like boron nanowires possess the microstructure of the outer oxidized cover layer and inner pure boron. The thickness of the outer oxidized cover layer is about 1-2 nm. It can provide useful information for the growth mechanism of boron nanowires. (C) 2002 Elsevier Science B.V. All rights reserved.