Highly toughened super high-impact polystyrene (HIPS)/organophilic montmorillonite (Org-MMT) nanocomposite was prepared by solution blending method. Organophilic modification of MMT layered silicate was achieved by using a special toughener-intercalant, quaternary ammonium salt of alpha-tertiary amine functionalized polybutadiene and shown by X-ray diffraction analysis. The resulting HIPS/Org-MMT nanocomposite was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), and static and dynamic mechanical analyses. The morphological study of HIPS/Org-MMT nanocomposite showed that nanolayers were exfoliated in nanocomposite and moreover caused much more well dispersed and reduced PS occluded rubber domains. This mechanism was found to be responsible for dramatic increase in toughness of nanocomposites. Additionally, improved thermal and dynamic mechanical properties of the resultant nanocomposite promises to open a new way for highly toughened super HIPSs via nanocomposite assemblies even with a very low degree of clay loading.