Abstract: Based on the principle of the angular momentum, equations of shaking moment in spatial linkages are derived, which consists of three terms: moment of grond bearing forces with respect to the reference point, ground bearing moments, and the reaction moment of input torque. In order to decrease the norm of shaking moment in a Shaking fore-balanced RS'SR linkage, the present paper develops two methods. In one method, optimum position vectors of counterweights of the ground links P₁^* and P₃^* along their respective rotation axes are determined in terms of the RMS shaking momnt. In the other, a balancing gear pair is utilized to further decrease the shaking moment. An example illustrates that the second method may decrase the shaking moment in the linkage more than the first one.