beta-Ga2O3 nanowires with different diameters were successfully synthesized by adjusting the size of catalyst via a simple thermal evaporation of elemental gallium powder in argon ambient. The size of catalyst was controlled by adjusting the sputtering time. The critical size of catalyst, which can be provided as a seed of nanowires, was investigated in detail. In this work, we have found that the growth mechanism of nanowires can be changed on the basis of catalyst size. The Ga2O3 nanowires synthesized by the vapor-liquid-solid (VLS) mechanism were successfully grown on the catalyst with a diameter not exceeding 65 nm. The HRTEM results indicate that the growth direction of nanowires synthesized by the VLS mechanism strongly depends upon the crystal direction of the catalyst. (C) 2008 Elsevier B.V. All rights reserved.