In this study, multiwalled carbon nanotubes (MWCNTs) and silica were used as hybrid fillers in natural rubber (NR) nanocomposites. The addition of MWCNTs and silica to NR was varied with the total filler loading fixed at 30 phr. The curing characteristics and mechanical, thermal, and morphological properties were investigated in this study. The results show that the scorch and curing time decreased as the MWCNT loading increased in the silica/MWCNT hybrid, but the maximum torque was increased by about 35%. The highest tensile strength was achieved at a loading ratio of 29 phr silica/1 phr MWCNTs. As the MWCNT loading increased in the silica/MWCNT hybrid, the tensile strength, elongation at break, and fatigue life decreased. However, the tensile modulus and rubber filler interaction increased. The scanning electron microscopy results show a good dispersion and better interaction between silica and the MWCNTs with the NR matrix at a 29/1 silica/MWCNT loading ratio. As the MWCNT loading ratio increased, the agglomeration of the MWCNTs became dominant and reduced the reinforcing effect of the MWCNTs. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013