Abstract: Polystyrene/nano-TiO2/hydrogenated styrene-ethylene-butylene-styrene copolymer composites were prepared via melt blending. The effects of amount of nano-TiO2 and SEBS on the mechanical properties, torque ternary and thermal properties of polystyrene were studied. The impact fracture microstructure of composites was observed using SEM. With increasing content of SEBS, the impact strength of polystyrene/nano-TiO2 composites increased and the tensile strength decreased. When the content of SEBS was 8 phr and the weight ratio of PS and nano-TiO2 was 97∶3, the mechanical properties were the best. The impact strength of the ternary composites was 5.626 kJ/m2, and the tensile strength was 25.623 MPa. Thermal performance of the ternary composites was increased by the addition of nano-TiO2 and SEBS. The maximum torque of the ternary composites decreased by 17 N·m compared with PS with an average torque being 7 N·m. The particles of SEBS embedded in the matrix resulted in a typical ductile fracture.