Poly (styrene-n-butyl acrylate-methyl methacrylate) (PSBM)/silica nanocomposite was prepared by emulsion polymerization in the presence of oleic acid surface modified nanosilica. The structure, morphology, size, and size distribution were characterized by Fourier transform infrared (FTIR), transmission electron microscopy (TEM), and dynamics laser scattering. The chemical bond was formed between PSBM and nanosilica revealed by FTIR and TEM studies. The composite particles with an averaged diameter ranging from 30 to 80 nm have the core-shell structure. The effect of silica content on the glass transition temperature T(g), pyrolyze temperature, and rheological behavior of PSBM composites was systematically investigated. The results indicated that the addition of nanosilica could effectively inhibit chain movement, and improved the pyrolyze temperature of PSBM. The steady viscosity and dynamic modulus were strongly dependent on the content and distribution of nanosilica in PSBM nano-composites. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 120: 3654-3661, 2011