The polystyrene modified organophilic montmorillonite clays (PS-OMMT) were preparation through intercalating styrene monomer into the layer of OMMT by in-situ polymerization. Composite modified asphalts with PS-OMMT and SBS were prepared by melt blending. Results showed the interlayer spacing of OMMT was increased by the intercalated polymerization reaction of styrene. The modified OMMT and SBS homogeneously disperse in the base asphalt, which lead to an improvement in terms of toughness, strength, and thermal stability. Impact of the PS-OMMT on the properties of SBS modified asphalt appears as a decreasing penetration, an increasing softening point, and a decreasing ductility. Compared with that of SBS modified asphalt, the anti-aging property of PS-OMMT /SBS modified asphalt was greatly improved.