Natural rubber vulcanizates were reinforced with in-situ formed silica particles in nano-scales of around 40 nm using a sol-gel process. The prepared sol-gel nanocomposites showed much higher London dispersive component of free energy compared with conventional melt-mixed composites. Also, much lower frictional coefficients were found for the sol-gel nanocomposites. The abrasion resistance of the nanocomposites was proven to be superior to that of melt-mixed composites.