Electrorheological properties of polyisoprene and polythiophene/polyisoprene blends were investigated for electroactive actuator applications. Experiments were carried out under the oscillatory shear mode and with an applied electric field strength varying from 0 to 2 kV/mm. The dynamic moduli, G' and G', of the pure polyisoprene were measured in terms of the crosslinking ratio and electric field strength. In the absence of an electric field, the storage modulus (G') increased but the loss loss modulus (G') decreased with increasing crosslinking ratio. In the uncrosslinked polyisoprene fluid, the storage modulus (G') exhibited no change in value with increasing electric field strength. For polyisoprene with crosslinking ratios of 2, 3, 5, and 7, the storage modulus sensitivity increased with electric field strength and attained maximum values of 10%, 60%, 25%, and 30%, respectively, at an electric field strength of 2 kV/mm. The dynamic moduli, G' and G', of blends of polythiophene with undoped particle concentrations of 5%, 10%, 20%, and 30% vol% were generally higher than those of crosslinked polyisoprene. The storage modulus sensitivity of these blends increased with electric field strength and attained maximum values of 50%, 35%, 110% and 45%, respectively, at an electric field strength of 2 kV/min. (c) 2006 Elsevier B.V. All rights reserved.