We prepared poly(styrene-b-butadiene-b-styrene) (SBS) matrix composites in which multiwalled carbon nanotubes (MWCNTs) were homogeneously dispersed, and their morphologies, thermal properties, and mechanical properties were investigated. The incorporation of MWCNTs into the SBS matrices improved their thermal and mechanical properties with appropriate flexibility. The MWCNT/SBS composites did not flow above 100 degrees C, and showed surprising improvements in terms of their creep properties. The results indicated the possibility of broadening their use in high temperature applications, and of significantly improving permanent strain, which are currently the main demerits of TPE. These drastic improvements in the various properties of MWCNT/SBS composites were assumed to have been caused by the formation of a three-dimensional structure at the interfacial phase of the SBS matrix along the MWCNTs, which we designated as a "cell structure".