Nanocarbons with a variety of morphologies were found after diamond nanoparticles (ND) were annealed at a low temperature. The conversion of ND to nanocarbons is a process of structural evolution that causes increase Of sp(2) bonding structure and decrease of sp(3) bonding structure in nanostructure. While being annealed, ND are converted to carbon onions and undergo phase transition in a series of ND -> bucky diamond -> carbon onions -> graphitic ribbons. The structural evolution of nanocarbons reflects the higher stability of planar graphitic ribbons over carbon onions. (c) 2006 Elsevier B.V. All rights reserved.