This paper reports the results of studies on the effect of phenol functionalization of carbon nanotubes (CNTs) on the mechanical and dynamic mechanical properties of natural rubber (NR) composites. Fourier transform infrared spectrometry (FTIR) indicates characteristic peaks for ether and aromatic rings in the case of phenol functionalized CNT. Although differential scanning calorimetric (DSC) studies show no changes in the glass-rubber transition temperature (Tg) of NR in the nanocomposites due to surface modification of CNT, dynamic mechanical studies show marginal shifting of Tg to higher temperature, the effect being pronounced in the case of functionalized CNT. Stress-strain plots suggest an optimum loading of 5 phr CNT in NR formulations and the phenolic functionalization of CNT does not affect significantly the stress-strain properties of the NR nanocomposites. The storage moduli register an increase in the presence of CNT and this increase is greater in the case of functionalized CNT. Loss tangent showed a decrease in the presence of CNT, and the effect is more pronounced in the case of phenol functionalized CNT. Transmission electron microscopy (TEM) reveals that phenol functionalization causes improvement in dispersion of CNT in NR matrix. This is corroborated by the increase in electrical resistivity in the case of phenol functionalized CNT/NR composites. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012