Abstract: Organic-inorganic nanocomposite, which is the complexof inorganic nanoparticleswiththe organic compound, is a popular research project in the nanoscale composite. The blending of different sorts of materials produces composite structures which can combine different material properties, or may reveal novel properties not existing in the constituent phases. In this issue, taking account of the problems in electrorheological fluids such as the high leakage current, low yield stress and stability, a novel type of electrorheological particleswhichwere composed of the polyaniline core and BaTiO3shell were prepared. As the core was made of polyaniline, the diameter and its distribution of ER particle (ERP) could be readily controlled. Furthermore, the polymer core contributed to the reduction of the density of ER particles, whichwas expected to prevent the sedimentation of the particles. The outer nonconductive layer, on the other hand, should have strong electronic resistance and excellent dielectric strength. In this sense, barium titanate was one of the best materials for the nonconductive layer. We had deposited BaTiO3layers on the particles bymeans of the sol-gel technique. The structure of particles was characterized byTEMand FT-IR; the influence of the thickness of barium titanate of the ERP on the ER effectswere studied in detail. The results showed that the ER effect of composite particleswas far stronger than that of pure polyanilineswhichwere synthesized by the same method, the thickness of BaTiO3thin filmhad an important influence on the ER effects and the optimum effectwas obtained atd=20 nm.