A new method is presented for preparing monodisperse and Uniform-size silica nanoparticles using a two-stage hydrolysis of silicon powder in aqueous medium. The influence of synthesis conditions including solution composition and temperature on the formation of silica nanoparticles were systematically investigated. The structure and morphology of the Silica Particles were characterized via transmission electron microscopy (TEM) and dynamic light scattering (DLS). Various-sized particles in the range 10100 non were synthesized. The size of the nanoparticles can be precisely controlled by using a facile regrowth procedure in the same reaction media. (C) 2008 Elsevier Inc. All rights reserved.