Colloidal silica forming nonspherical particles cluster, whose long axis/short axis ratio of silica particles is of 1.2 to 20, and average long axis/short axis ratio of 3 to 15. This colloidal silica can be produced by forming particles by adding basic nitrogen compounds to an active silicic acid aqueous solution, the solution which produced by hydrolysis of tetraalkoxysilane, while heating, then growing particles by using a build up method.