Abstract: Nearly monodispersed silica nanoparticles with controllable sizes ranging from 90 nm to 200 nm were synthesized via a solgel process by improving a classic Stber method. The effects of the silica precursor (tetraethylorthosilicate, TEOS), solvent, catalyst (NH4OH) and stirring speed on the finite size control of the silica nanoparticles were investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results showed all these factors had significant effects on the size and size distribution of the silica particles. A good monodispersity can be obtained and the size variation can be controlled within 20 nm.