Characterization of optimal silica sol synthesized by the sol-gel method have been investigated as a function of the mole ratios of starting materials and reaction temperature. Reaction completion time was exposed to measure the OH/CH ratio as reaction time at 25℃. In 50 to 60 minutes, the reaction was completed at approximately a 1:1 ratio for OH/CH that reached the equilibrium state. The beginning point and ending point of hardening were measured through TGA investigation of the sol solution. The hardening of the sol solution was completed in 7 minutes and viscosity was maximum from 4 to 5 minutes and set at 9 minutes.