Two types of SBS/OMMT composites are prepared by melt blending using a twin-screw extruder. An X-ray diffractometer indicates that polymer chains have intercalated into the gallery of the clay. It is shown in TEM photos that the thickness of the layer aggregate in the SBS1301 matrix is approximately 200 A, but in the SBS4402 matrix the size of the filler particle is in micrometers. When SBS1301 is intermingled into SBS4402/OMMT, the particle size is reduced obviously. The tensile strength and elongation at break of the nanocomposite, SBS1301/OMMT, increase with the addition of OMMT; and when addition is 5phr, they achieve maximum. A small content of OMMT (less than 5phr) can prevent the deterioration of the mechanical properties of the SBS1301/MMT. In addition, a small content of SBS4402 (less than 20 wt %) can improve the mechanical properties of the SBS1301/OMMT composites. (c) 2005 Wiley Periodicals, Inc.