(Problem) This invention provides a high-purity, high-concentrated silica sol with long-term stability and low viscosity by preventing viscosity-increase after production, and method for producing the same. This invention provides the high-purity and high-concentrated silica sol that does not undergo a viscosity-increase or gelation in spite of any particle size differences of silica. This is obtained by adding a dispersing agent at a specific concentration to the reaction solution or solvent substitution-concentrated solution in the production process. (Means to Solve Problems) A silica sol produced by an alkoxide method, wherein said silica sol comprises at least a dispersing agent and silica, wherein said dispersing agent concentration is 10-3000 ppm with respect to the silica, wherein said dispersing agent consists of one or more compounds selected from inorganic acid, inorganic acid salt, organic acid and organic acid salt whose degradation temperature and boiling point are both 60.degree. C. or higher, wherein said silica sol has a silica concentration of 20 weight % or higher, and method for producing the same.