Titanium dioxide (TiO2) powders were synthesized by using TiO2 colloidal sol prepared from titanium-tetraisopropoxide (TTIP) and used as a starting material by applying the sol-gel method. The effect of aging times and temperatures on physical and chemical properties of TiO2 sal particles was systematically investigated. The results showed that the crystallinity and average particle size of TiO2 can be successfully controlled by adjusting the aging time and temperature. The samples after calcination of TiO2 powders were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and nitrogen adsorption measurements. In addition, the photocatalytic activity of synthesized TiO2 powders was evaluated by studying the degradation of 10 ppm aqueous methylene blue dye under 32 W high pressure mercury vapor lamp with 100 mg of TiO2 powders. The highest photocatalytic activity was observed in TiO2 powder synthesized at 90 degrees C for 0 h attributed to the presence of anatase and rutile phases in an 80:20 ratio. (C) 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.