This paper described the influence of the degree of interaction between silane coupling agents and polymers on the viscoelastic properties of silica-filled rubber.The degree of interaction was determined by the tensile modulus and the change of tanδ of green and vulcanized compounds. It was found that the tensile modulus was highest with MPTES (mercaptopropyltriethoxysilane) and lowest with OTES (octyltriethoxysilane). TESPD (bis(triethoxysilylpropy) disulfide) laid in between. These results were attributed to the difference of the reactivity with polymers and silane coupling agents, where the change of tanδ of green and vulcanized compounds was biggest with MPTES and smallest with OTES. In other words, it was suggested that the lower tanδ of MPTES was caused by higher degree of interaction between the silane coupling agent and the polymer.