<p>A homogeneous electro rheological fluid of the invention comprises a poly( alpha -amino acid) or a poly( gamma -glutamate), and an electric insulating liquid in a specific amount. To provide a homogeneous electro rheological fluid of good stability, with long lasting and consistent performance in the presence of a trace of water. The fluid also exerts a good electro rheological effect wherein a hydrocarbon oil or an ester-type oil is used as an electric insulating liquid.</p>
