A novel silica which is in the form of ultrafine particles having mesopores and has a regular structure; and a process for producing the silica. The silica is a self-organized nanoparticulate silica characterized in that the average particle diameter is 4 to 30 nm, preferably 6 to 20 nm, and these particles are regularly arranged so as to form a primitive cubic lattice. The self-organized nanoparticulate silica is produced by mixing an alkoxysilane with an aqueous solution of a basic amino acid, reacting the mixture at 40 to 100° C., and subjecting the reaction mixture to drying and preferably to subsequent burning. Also provided is a process for producing fine silica particles having a particle diameter of 4 to 30 nm, which comprises mixing a solution of an alkoxysilane compound having 1 to 4 alkoxy groups with a solution of a basic amino acid and reacting the mixture at 20 to 100° C. to cause hydrolysis and condensation polymerization.