Nanocomposites were prepared with different grades of nitrile rubber with acrylonitrile contents of 19, 34, and 50%, with styrene-butadiene rubber (23% styrene content), and with polybutadiene rubber with Na-montmorillonite clay. The clay was modified with stearyl amine and was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The XRD studies showed an increase in the gallery gap upon the modification of the filler by stearyl amine. The intercalation of the amine chains into the clay gallery gap was confirmed by the presence of some extra peaks (2928, 2846, and 1553 cm(-1)) in the FTIR spectra. The clay-rubber nanocomposites were characterized by TEM and XRD. The mechanical properties were studied for all the compositions. An improvement in the mechanical properties with the degree of filler loading up to a certain level was observed. The changes in the mechanical properties, with changes in the nature and polarity of the rubbers, were explained with the help of XRD and TEM results. (C) 2004 Wiley Periodicals, Inc.