A method was proposed for the preparation of silica powders using inexpensive material of sodium silicate (Na2SiO3) and carbon dioxide (CO2) by pressured carbonation, in which carbon dioxide acted as a precipitating reagent. Microstructure and size analyses of the precipitated silica powders were carried out using transmission electron microscopy and dynamic light scattering. The average particle size, size distribution and yield of silica powders were affected by reaction time, temperature and concentrations of surfactant and sodium silicate solutions. The particle size of silica powders increased with reaction temperature and concentration of sodium silicate, and the yield of silica powders increased with increasing reaction time. The size distribution of silica powders was affected by concentration of surfactant PEG. The optimal preparation conditions were experimentally determined for obtaining the silica powders with nanometer size, narrow size distribution, spherical shape and high purity without sodium carbonate and surfactant. (C) 2009 Elsevier B.V. All rights reserved.