Natural rubber (NR), polyurethane rubber (PUR), and NR/PUR-based nanocomposites were prepared by adding a pristine synthetic layered silicate (LS; sodium fluorohectorite) in 10 parts per hundred parts rubber, following the latex compounding route. The dispersion of the LS latices in the composites was studied by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The morphology-dependent dielectric properties of the produced nanocomposites were examined using broad-band dielectric spectroscopy (BDS) at ambient temperature. Besides the glass/rubber transition of the polymer matrices, interfacial polarization (IP) is evident in the produced nanocomposites. The alpha-relaxation, as well as the beta-mode, in the PUR-containing nanocomposites proved to be less affected by the presence of LSs. The obtained experimental data suggest that the LS is more compatible with and thus better intercalated by the FUR than by the NR which was prevulcanized in this case. (C) 2007 Wiley Periodicals, Inc.