Alumina (Al2O3) nanostructures were grown in a horizontal Al2O3 tube furnace by chemical vapor deposition (CVD) using an aluminum (Al) powder source without catalysts at temperatures ranging from 1100 to 1400 degrees C and pressures ranging from 0.01 to 53.32 kPa. As the temperature and pressure were increased, the nanostructure size increased and in particular, increasing pressure resulted in various changes in morphology. Here we present a morphology diagram of the one-dimensional Al2O3 nanostructure growth to illustrate different growth features at various temperatures and pressures. Moreover, we suggest that the Al2O3 nanostructure deposition mechanism was affected by the liquid source droplet and film morphology as the temperature and pressure changed in the absence of catalysts. (C) 2012 Elsevier B.V. All rights reserved.