The effect of coupling agent silane Si69 on properties of nanocomposites of nature rubber with different sized nano-silica (15, 30 and 80 nm)was investigated in terms of curing performance, mechanical properties, Mullins effect, Payne-effect, loss factor, the dynamic heat build-up and dynamic mechanical property etc. while taking the same composites without coupling agent as comparison. Results show that with the addition of the coupling agent Si69, the dispersity of nano-silica in the rubber and the binding of nano-silica with the rubber matrix were improved; the mechanical properties of nano-silica/nature rubber composite were effectively enhanced and the positive sulfuration time t₉₀ was shortened. It is noted that the smaller size of the nano-silica is, the better positive effect on the performance and mechanical properties of the composite can be obtained. Due to the addition of the coupling agent Si69, the Payne-effect, loss factor and the dynamic heat build-up can be reduced for the composites with nano-silica of 15 nm and 30 nm, respectively, but is not obvious for the ones with 80 nm silica.