Nucleation and growth of SiO₂ particle in the SiO₂ supersaturation solution, which was synthesized with TEOS by sol-gel method, were investigated. When the TEOS solution was fed into the semi-batch reactor containing the ammonia solution at constant flow rate, the concentration of silane produced by hydrolysis and condensation of TEOS and particle induction time were measured and then the supersaturation of SiO₂ in the solution was estimated. For investigation of dependency of nucleation and growth rates of SiO₂ particle on the supersaturation in the solution the concentration of the ammonia catalyst was varied. The reaction rates or hydrolysis and condensation of the TEOS was changed with the ammonia concentration and it resulted in variation of the supersaturation of SiO₂ in the solution. The induction time and supersaturation was reduced with increase of the ammonia concentration due to facilitation of the hydrolysis and condensation reaction. Thus, the lower population density and larger size of final particles were obtained with the higher ammonia concentration. To predict the particle nucleation and growth rates from measurable variables of SiO₂ supersaturation and particle induction time with change of TEOS reaction condition the model equations were suggested. From the comparison between experimental data and model prediction the exponential constant for particle nucleation rate was suggested as -634.02. This result meant that the particle nucleation rate was reduced with decrease of the induction time and the particles were induced at different supersaturation. In addition, the model prediction for the final mean particle size was well agreed with experimental data.