The electrorheological (ER) and dielectric properties of PPy-silica nanocomposite suspensions in silicone oil were investigated. Various PPy-silica nanocomposite particles were synthesized by suspension polymerization in the presence of silica nanoparticles controlling the ratio of silica/pyrrole during the polymerization. The ER response and the particle conductivity increased with the increase in the silica/pyrrole ratio, indicating that the increased particle polarization plays a role in enhancing the ER response. The dielectric properties of PPy-silica nanocomposite particles and their suspensions support that the enhanced ER response with the increase in the silica/pyrrole ratio arises from the enhanced polarization, which originates from the increased particle polarization.