Star-shaped and linear block thermoplastic poly(styrene-b-butadiene) copolymer (SBS)/organophilic montmorillonite clays (OMMT) were prepared by a solution approach. The intercalation spacing in the nanocomposites and the degree of dispersion of nanocomposites were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The mechanical properties, dynamic mechanical properties, and thermal stability of these nanocomposites were determined. Results showed that SBS chains were well intercalated into the clay galleries and an intercalated nanocomposite was obtained. The mechanical strength of nanocomposites with the star-shaped SBS/OMMT were significantly increased. The addition of OMMT also gave an increase of the elongation, the dynamic Storage modulus, the dynamic loss modulus, and the thermal stability of nanocomposites. The increase of the elongation of nanocomposites indicates that SBS has retained good elasticity. (C) 2004 Wiley Periodicals, Inc.