Abstract Electro-rheological (ER) fluids can change from a liquid state into a solid-like gel under electrical potential. This change takes place within milliseconds and it is reversible once the electrical potential is removed. The proposed design in this investigation employs the unique characteristics of ER fluids to vary the damping of a tuned absorber. Numerical predictions from a simple model, and corresponding experimental observations are presented. ER fluids hold great promise in vibration control applications.