The effect of particle size on the zeta potential and theology of nanoparticulate SiO2 dispersions stabilized with the polymer polyethylenimine (PEI) was investigated experimentally, The particle size and molecular weight of the polymer had only a small influence on the amount of PEI needed and the achieved zeta potential of the suspensions. The polymer concentration range within which a stable dispersion could be produced was very narrow for the smallest particle size. Higher-molecular-weight PEI was more suitable to stabilize small particle dispersions. Under optimum conditions, Newtonian flow behavior was achieved for dispersions of 20 nm particles with a solids content as high as 25 vol%.