A stable aqueous nanocomposite dispersion containing cellulose whiskers and a poly(styrene-co-hexylacrylate) matrix was prepared via miniemulsion polymerization. We were able to prepare a stable dispersion with a 20 wt % sohd content and a cellulose whiskers content ranging from 1 up to 5 wt % based on polymer content. To avoid particle agglomeration leading to coagulum formation, the addition of a low amount of reactive silane, i.e., methacryloxypropyl triethoxysilane revealed to efficiently stabilize the dispersion. The nanocomposite dispersion was characterized using dynamic light scattering, transmission electron microscopy, and atomic force microscopy. Films obtained by casting followed by water evaporation and particle coalescence were analyzed by differential scanning calorimetry, dynamic mechanical analysis, and tensile testing. At 5 wt % whiskers loading, an enhancement by 500% of the storage modulus above the glass transition was determined. (C) 2009 Wiley Periodicals, Inc. J Appi Polym Sci 114: 2946-2955, 2009