TiO2 nanoparticles were introduced into high-impact polystyrene (HIPS) in the form of a master batch in which TiO2 was predispersed in composites of HIPS and ethylene-vinyl acetate copolymer (EVA) by melt compounding. The resulting materials were analyzed with a Rosand Precision rheometer, transmission electron microscopy, atomic force microscopy, and Ultraviolet-visible light spectrophotometry. The results showed that the introduction of TiO2 nanoparticles into HIPS influenced the apparent viscosity of the composites to a rather small extent. The addition of EVA could regulate the rheological behavior of the HIPS/TiO2 master batch greatly. EVA helped the dispersions of the agglomerates of TiO2 nanoparticles in the flow; this was featured by the distinct yielding in the flow after the introduction of EVA, as well as the large change in the non-Newtonian indices. The dispersions of the HIPS/TiO2 master batch in the HIPS matrix were improved greatly by the addition of EVA. TiO2 nanoparticles were dispersed randomly in HIPS/EVA/TiO2 nanocomposites. The dispersion improvement of the HIPS/EVA/TiO2 master batch was also proved by atomic force microscopy and ultraviolet-visible spectroscopy investigations. The mechanical properties of HIPS/EVA/TiO2 nanocomposites with low TiO2 contents were slightly higher than those of pure HIPS. (c) 2006 Wiley Periodicals, Inc.