Formation of silica gel through hydrolysis and successive condensation of tetraethoxysilane (TEOS) is studied in the presence of NH3 as a basic hydrolysis catalyst. The rate of hydrolysis of TEOS was determined by gas chromatography. Dependence of the hydrolysis rate on the initial composition of the reaction mixture is examined in detail; the rate showed first order kinetics for TEOS concentration, and the apparent reaction orders with respect to NH3, and H2O are estimated as 1.1, and 1.4, respectively. The particle diameter and numeric concentration of silica gel formed was measured by the dynamic light scattering method. A very narrow distribution of the particle diameter was observed during the growth, showing the formation of monodispersed silica particles. Simulation of the rate of particle growth using the kinetic data above reveals that the hydrolysis of TEOS is the rate determining step. Calculated values of numeric concentration of the particles are in good agreement with experimental values.