ZnO nanostructures with different morphologies were synthesized through a direct melt oxidation of source materials mixed with Al and Zn in air at atmospheric pressure. When Al-Zn mixture was used as a source material, tetrapod-shaped ZnO nanostructures were formed. ZnO nanostructures with bottle and tubular shape were fabricated when Al-Zn source material contained Au. The morphology depended on the Au content in Al-Zn source material. In addition, when carbon was contained in Al-Zn source material, ZnO nanostructures with comb shape were observed after the oxidation of the source material. All the ZnO nanostructures showed a hexagonal wurtzite crystallographic structure and were grown along the  direction. On the other hand, the green emission centered at 510 nm was detected for all the ZnO nanostructures. This suggests that the ZnO nanostructures had high density of oxygen vacancies, which is supposed to be ascribed from high density of surface and subsurface oxygen vacancies in the nanostructures.