Polymer chains are grafted from silica beads (colloidal sol in dimethylacetamide) by atom transfer radical polymerization (ATRP). The method consists of grafting first the initiator molecules on the silica surface ("grafting from" method), in two steps. First, thiol-functionalization of the surface was achieved via silanization with a mercaptopropyl triethoxysilane. Second, we performed an overgrafting of the surface by reacting the thiol with 2-bromoisobutyryl bromide to generate the halogen-functional ATRP initiator. From that, the polymerization of styrene was conducted. Control of both the molecular weight and the density of grafted chains can be achieved by this method. The other originality of this work is that we keep the nanoparticles in solution at each stage of the procedure (even during the purification steps), as this is the only way to avoid irreversible aggregation. The state of dispersion of the grafted nanoparticles is followed by small-angle neutron scattering. Characterizations such as gel permeation chromatography, Si-29 CP/MAS NMR, elemental analysis, infrared spectroscopy, and then mogravimetric analysis are conducted to confirm the success of the grafting reaction.