A practical and effective semi-active on-off damping control law using semi-active actuators is developed for vibration attenuation of a natural, multi-degree-of-freedom suspension system, when its operational response mode is specified. It does not need the accurate system parameters and semi-active actuator dynamics. It reduces the total vibratory energy of the system including the work done by external disturbances and the maximum energy dissipation direction of the semi-active actuator is tuned to the operational response mode of the structure. The effectiveness of the control law using a single semi-active linear mount is illustrated with a three-degree-of-freedom excavator cabin suspension model. (C) 2002 Elsevier Science Ltd. All rights reserved.