Silica sol (English name: Silica solution) is a colloidal solution, odorless and non-toxic. Silica sol is a dispersion of nano-sized silica particles in water or solvent. Since the SiO2 in silica sol contains a large amount of water and hydroxyl groups, silica sol can also be expressed as SiO2·nH2O.

There are different methods for preparing silica sol. The most commonly used methods include ion exchange, one-step hydrolysis of silicon powder, and hydrolysis of silane.