Abstract: A novel method was developed to prepare monodisperse ultrafine silica using ammonia as a catalyst by means of hydrolysis of tetraethoxysilane（TEOS）.Polyvinylpyrrolidone（PVP） can effectively reduce the silica particles size.It was found that the size of monodisperse silica particles tends to decrease with increase of the PVP concentration.By using the optimum process parameters,monodisperse silica nanoparticles with diameter 11nm were prepared.Furthermore,these monodisperse silica spheres can be successfully used as seeds in the regrowth procedure in the same reaction media.The size of the particles can be precisely controlled by addition various TEOS concentration.