Aluminum oxide nanoparticles (Al2O3) were prepared and the obtained structure and size of the prepared Al2O3 nanoparticles were studied via X-ray diffraction (XRD) and transmission electron microscopy. The effect of adding various concentrations of the Al2O3 and gamma radiation on the structural and optical properties of syndiotactic polystyrene (sPS) were investigated using XRD and UV-spectroscopy. XRD data showed that the addition of the various concentrations of the Al2O3 influenced the crystallinity of the nanocomposites. A significant change in the lattice structure and the optical parameters were observed. The results showed that a sample with the Al2O3 concentration of 10% achieved a higher refractive index and optical conductivity. Effect of gamma irradiation on sPS sample loaded with 10% Al2O3 was studied. The results showed several changes in the structure and optical properties of the resulting films due to crosslinking between the polymer chains. This result reflects that the polymer suffered from structural rearrangement due to the irradiation treatments. POLYM. ENG. SCI., 59:555-565, 2019. (c) 2018 Society of Plastics Engineers