A TiO2 nanostructure was synthesized via a simple method using only concentrated hydrochloric acid as the morphological/crystallographic controlling agent. Microscopy images showed that the texture of the TiO2 powder could be easily engineered and tuned by tailoring the HCI volume, creating cuboid, flower, cauliflower, and ball-shaped particles. Three-dimensional TiO2 microparticles resulted from the self-assembly of nanostructured sub-units including nanocubes, nanoprisms, and nanorods. The crystalline anatase and rutile phases were also identified depending on the acidic medium. HCI played a key role in orchestrating the structures and morphologies of the TiO2 nanoscale materials. The phase transformation and morphological changes were strongly related to the crystal growth mechanism of the TiO2 nanostructure. (C) 2009 Elsevier B.V. All rights reserved.