Ga2O3 nanomaterials were synthesized from mechanically ground GaN powders with thermal annealing; Ga2O3 nanobelts were formed in a nitrogen atmosphere, while Ga2O3 nanoparticles were formed in an oxygen atmosphere. The structural properties of the Ga2O3 nanomaterials were investigated by X-ray diffractometer (XRD) and high-resolution transmission electron microscope (HRTEM). The study of field emission scanning electron microscopy (FESEM) on the microstructures of nanomaterials revealed that the nanobelts are in the range of about 10-200 nm width and 10-50 nm thickness, and that nanoparticles are in the range of about 20-50 nm radius. On the basis of XRD and HRTEM data, we determined that the nanobelts grow toward a direction perpendicular to the (010) lattice plane and that they are enclosed by facets of the (101) and (101) lattice planes. The formation of the nanobelts may be described by the vapor-solid (VS) mechanism, and the supersaturation degree of gaseous phase may play an important role in the formation of Ga2O3 nanomaterials. (C) 2002 Elsevier Science B.V. All rights reserved.