Abstract: Electro rheological fluids were selected as the active vibration control of smart composite structures. The experimental investigations were focused on evaluating the elasto-dynamic response charact eristics of beams featuring electror heological fluids when the beams were subject ed to forced vibration. Meantime, the active vibration control of smart composite beams is studied. The results of these considerations clearly demonstrate the ability to significantly change the vibrational characteristics of beams fabricated in smart composites by changing the electric field imposed on the fluid domain. A conclusion is made that the shear modulus of ER fluids can be controlled by the application of an electric field to the ER material.