In this work, the surface defect (Ti3+) controlling on anatase TiO2 nanocrystal has been reported and compared to the common methods which must prepare the crystalline TiO2 in the first step prior to the creation of surface defect in the second step. In this work, we have been successful to create the surface defect in first step, at mild temperature in the absence of reduced gas, at the same time with the preparation of crystalline TiO2 in anatase phase by sol-gel technique. The formation of surface defect is explained as the result of removing i-OR from Ti4+ site during crystallization by calcination process, so that the oxygen vacancy site (Ti3+) was formed. The number of i-OPr which formed from the partial reaction of precursor as an alkoxide was controlled by decreasing the molar ratio of water: alkoxide (165, 80, 40, 16, and 4) during sol-gel synthesis under ultrasonic irradiation. The improving of bulk structure was also observed after the creation without phase transformation and significant surface area. (C) 2008 Elsevier B. V. All rights reserved.