In the present study, the phase stability of spherical silica particle dispersion was investigated experimentally. The silica particles were synthesized by the sol-gel method and stabilized by electrostatic and steric stabilization. For a given pH, the silica particles were coagulated at a certain critical salt concentration, which depended on the chemical nature of the added salts. The critical coagulation concentration showed that the particle zeta-potential in the presence of electrolytes, such as NaCl, NaBr,and KCl, had no appreciable influence on the stability of silica dispersion. The aggregate sizes measured by dynamic light scattering gave useful information on the coagulation process in the presence of the electrolytes. The critical coagulation concentration of a salt containing sodium decreased monotonically as pH increased. Meanwhile, the phase stability in the presence of K+ ions was the worst at the pH 8.5. In addition, the zeta-potential that showed a strong dependence on pH in the presence of Na+ ions was a very weak function of pH in the presence of K+ ions.