Abstract: Unbalanced oscillatory pressures, developed on the power piston of hydraulic servoactuator systems cause vibrations on actuator housing supports. An unbalanced oscillatory force results, when two sides of the power piston are subjected to two unequal oscillatory forces induced by a disturbance. The two important disturbances are: pump flow rate oscillations, caused by power source torque oscillations; and, load oscillations. The invention is a hydraulic actuator connected in parallel to the power piston and designed to cancel vibrations by eliminating the unbalanced oscillatory pressure on the power piston. This is accomplished by designing the piston frequency of the invention, defined as tuning frequency, to be equal to the unbalanced oscillatory pressure frequency.