Controlling the nanocrystalline structure of TiO2 powders is very important for the application to dyesensitized solar cells (DSSC) because the efficiency of DSSC is considerably influenced on the change of the TiO2 nanostructures. Nanocrystalline TiO2 powders were synthesized by the conventional sol-gel method, in which titanium iso-propoxide was reacted under various acid conditions. As-prepared TiO2 powders were calcined at 600 degrees C for 5 h. The structural informations of the calcined TiO2 powders were in detail characterized by X-ray diffraction, nitrogen adsorption isotherm, and electron microscopy. The structural analysis of as-prepared TiO2 powders supported that their crystal structures were changed by the variation of acid solutions. In order to study the structural variations of the TiO2 powders, some acid solutions were prepared with the selected mixtures of H2SO4, HCl, and HNO3. The nanocrystalline properties such as crystal type and porosity were mainly affected by the use and the amount of H2SO4. (C) 2010 Elsevier B. V. All rights reserved.