Surface functionalization of multiwalled carbon nanotubes is carried out by acid treatment followed by reaction with multifunctional silane, 3-aminopropyltriethoxysilane. The chemical interaction of silane with the oxidized nanotube surface is confirmed by Fourier transform infrared spectroscopy (FT-IR). Energy dispersive X-ray analysis (EDX) studies also indicate the presence of silane on the surface of the carbon nanotubes. X-ray diffraction reveals the change in the crystalline phases due to surface functionalization. Raman spectroscopy of the acid treated CNT further corroborates the formation of surface defects due to the introduction of carboxyl groups. Thermogravimetric analysis of the functionalized CNT exhibits a multiple peaks in the temperature range of 200–650 °C that corresponds to the degradation of chemically grafted aminosilane on the CNT surface. The influence of silane functionalized carbon nanotubes on the rheometric and mechanical properties of natural rubber vulcanizates is investigated. Rheometric properties like scorch time and optimum cure time increases. Modulus and tensile strength increase due to higher polymer-filler interaction between the carbon nanotube and NR vulcanizates.