A rigid-rod aromatic poly (pyridinium salt) was synthesized and doped with iodine (I2) for making anhydrous electrorheological (ER) fluids. The I2-doped particles were farther processed into ones having insulating skins. Dielectric properties and current densities of the suspensions containing these particles were studied to elucidate the roles of conductivity of the dispersed phase in the ER suspension.