A series of polystyrene hybrid nanocomposites have been fabricated with varying amounts of TiO2 viz., 0, 0.5 and 1 % w/w along with 3% TS by in-situ polymerization method. The influence of surface modified TiO2 nanoparticles on the thermal properties of PS matrix was examined using thermogravimetry and differential scanning calorimetry. Thermal characteristics of the polystyrene/TS/TiO2 hybrid nanocomposites were evaluated by using differential scanning calorimetric (DSC), thermal analysis (DTA), thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMA). By comparison with the values obtained for the hybrid mixed composites, the thermal properties of 1wt. % TiO2 along with 3wt.% TS are increased. On the other hand, PS/TS/TiO2 nanocomposites have higher glass transition temperature and better thermal and thermo oxidative stability than the bare PS. The morphological behaviors of the prepared polystyrene/TS/TiO2 were analyzed using SEM.