The preparation of high-dielectric poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) composites containing functionalized single-walled carbon nanotubes (f-SWCNTs) noncovalently appended with dibutyltindilaurate are reported herein. Transmission electron microscopy and X-ray photoelectron and Raman spectroscopy confirmed the noncovalent functionalization of the SWCNTs. The SEBS-f-SWCNT composites exhibited enhanced mechanical properties as well as a stable and high dielectric constant of approximately 1000 at 1 Hz with rather low dielectric loss at 2 wt% filler content. The significantly enhanced dielectric property originates from the noncovalent functionalization of the SWCNTs that ensures good dispersion of the f-SWCNTs in the polymer matrix. The f-SWCNTs also acted as a reinforcing filler, thereby enhancing the mechanical properties of the composites. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013