Hybrid nanocomposites of polystyrene (PS) and TiO2 were prepared by the facile surface thiol-lactam initiated radical polymerization (TLIRP). At first, the surface of TiO2 nanoparticles was modified by 3-mercaptopropyl-trimethoxysilane to prepare TiO2-SH. Subsequently, a radical polymerization of styrene was accomplished in the presence of TiO2-SH and butyrolactam to afford PS-g-TiO2 nanocomposites. The nanocomposites were investigated by H-1-NMR, FT-IR, GPC and XPS. The morphology of the nanocomposites was captured on TEM images, showing the encapsulation of TiO2 with PS. The TGA data suggest that the thermal stability of PS was enhanced upon inclusion of TiO2 nanoparticles. The dispersability of TiO2 nanoparticles was improved significantly after functionalization of PS chains.