Monodisperse polystyrene (PS) nanoparticles with a size of 190 nm were first synthesized by emulsion polymerization. Then PS/titanium dioxide (TiO₂; core/shell) nanocomposite particles were prepared by coating TiO₂ nanoparticles on the surface of the PS nanoparticles using aqua ammonia/triethanolamine as the positive/negative catalyst pair. Roughness degree of the surface of the shell of the PS/TiO₂ nanocomposite particles increased with increasing amounts of aqua ammonia or triethanolamine. Morphology of the surface of the TiO₂ shell can be regulated by changing the amounts of aqua ammonia and triethanolamine synchronously. The PS/TiO₂ nanocomposite particles obtained at 2.00 g/0.10 g, 3.00 g/0.20 g and 5.00g/0.40 g of aqua ammonia/triethanolamine showed good morphology of the surface of the TiO₂ shell. Roughness on the surface of the TiO₂ shell was remarkably heightened when the reaction temperature of the hydrolysis and condensation process was increased from 50°C to 70°C.