A colloidal silica comprising, silica particles inside of which or on the surface of which a nitrogen containing alkaline compound is fixed, wherein said silica particles are prepared by forming and growing colloid particles using the nitrogen containing alkaline compound. Said colloidal silica can be prepared by preparing active silicic acid aqueous solution contacting silicate alkali aqueous solution with cation exchange resin, adding the nitrogen containing alkaline compound and heating, and then growing up particles by build-up method.