Organically modified and unmodified montmorillonite clays (Cloisite NA, Cloisite 30B and Cloisite 15A), sepiolite (Pangel B20) and nanosilica (Aerosil 300) were incorporated into hydrogenated nitrile rubber (HNBR) matrix by solution process in order to study the effect of these nanofillers on thermal, mechanical and dynamic mechanical properties of HNBR. It was found that on addition of only 4 phr of nanofiller to neat HNBR, the temperature at which maximum degradation took place (T-max) increased by 4 to 16 degrees C, while the modulus at 100% elongation and the tensile strength were enhanced by almost 40-60% and 100-300% respectively, depending upon nature of the nanofiller. It was further observed that T-max was the highest in the case of nanosilica-based nanocomposite with 4 phr of filler loading. The increment of storage modulus was highest for sepiolite-HNBR and Cloisite 30B-HNBR nanocomposites at 25 degrees C, while the modulus at 100% elongation was found maximum for sepiolite-HNBR nanocomposite at the same loading. A similar trend was observed in the case of another grade of HNBR having similar ACN content, but different diene level. The results were explained by x-ray diffraction, transmission electron microscopy, and atomic force microscopy studies. The above results were further explained with the help of thermodynamics. Effect of different filler loadings (2, 4, 6, 8, and 16 phr) on the properties of HNBR nanocomposites was further investigated. Both thermal as well as mechanical properties were found to be highest at 8 phr of filler loading. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1428-1441, 2010