A propanol sol of silica having a specific surface area of 25 to 550 m.sup.2 /g, the sol having an SiO.sub.2 concentration of 10 to 50% by weight of SiO.sub.2 and a residual content of a medium containing 7.5% by weight or less of water based on the SiO.sub.2 content and 90% by weight or more of propanol, is prepared by an improved process involving replacing the aqueous medium in an acidic aqueous sol of silica containing 5 to 50% by weight of SiO.sub.2 and a medium having a water content of 15% by weight or more with propanol by an atmospheric distillation method in which a concentration of 5 to 50% by weight of SiO.sub.2 in the sol and 1 to 85% by weight of methanol in the medium in the sol is maintained when the medium in the sol during the replacement contains 15 to 0.5% by weight of water.