Abstract: Electrorheological fluids are new intelligentmaterials. They are of great significance to study the viscoelasticproperties of ER devices in an electric field. In this paper,forced ocsillation experiments of electrorheological fluids have been studiedby HAAKE RS600 rheometer and the changes of ERF storage modulus, lossmodulus and loss factor with shear stress and shear frequency areobtained for different shear stress rates and oscillation frequencies.