Boehmite particles modified with organic ligands were prepared through the reaction of boehmite with acrylic acid or diethylphosphoric acid (formed in situ from triethyl phosphate). The chemical structures of these particles were determined, and it was shown that they formed stable aqueous dispersions with a particle size lower than 200 nm (average diameter = 40-100 nm, depending on the method of modification) for more than 90% of the population. These nanoparticle dispersions were mixed with carboxylated styrene-butadiene latex, and after water evaporation, homogeneous composites were obtained when the modifier concentration was in the range of 0.5-3 wt %. The mechanical properties of the composites were improved with respect to those of the unmodified rubber (tensile strength up to 200% and elongation at break up to 40%). The modifiers also improved some mechanical properties of rubbers cured with sulfur /N-cyclohexylbenzothiazole-2-sulfenamide/ZnO/stearic acid or ZnO/stearic acid systems. (C) 2007 Wiley Periodicals, Inc.