Crystalline alumina nanowires were synthesized at elevated temperatures in a catalyst-assisted process using iron as catalyst. Nanotrees that formed by alumina nanowires were also found. SEM shows that typical nanowires are around 50 nm in diameter and around 2 mum in length. The tree trunk of the nanotrees are around 100 nm in diameter and around 10 mum in length. HRTEM with electron diffraction study reveals that the nanostructures are crystalline. The EDX confirms that the nanostructures contain only elements of Al and O. The XRD study shows that the nanowires are alpha-Al2O3. The results are explained in the light of growth mechanism based on a vapor-liquid-solid (VLS) process. (C) 2002 Elsevier Science B.V. All rights reserved.