Abstract: A concept of independent active balancer for dynamic balancing of planar mechanisms was proposed, the main idea of which is to balance the mechanisms actively by introducing a control system with little changes to their original structures and motions. The proposed balancer was composed of a two DOF linkage and a controllable motor. One of the two input shafts of the linkage acts as the output shaft synchronously, which is connected to the input shaft or the output shaft of the mechanism to be balanced and rotates at the same speed. The other input is driven by the control motor. Because of the special configuration, the balancer can be considered as an intelligent balancing box with one extended shaft outside which can be attached to a machine easily and meet different balancing requirement by adjusting its structural and control parameters. The conceptual design of the balancer was discussed and several feasible schemes based on the planar linkages were obtained. Taking one scheme as an example, the design procedure of the active balancer was described. Finally, numerical examples were given to demonstrate the effectiveness of the proposed balancer. The balancing effects of different schemes of the active balancer and the existing dyad method were compared. The results show that the introduced control system provides the active balancer with more flexibility and better balancing effect than the adding dyad method. For different balancing object, one or more dynamic effects can be reduced by selecting suitable structural parameters of the linkage and speed trajectory of the control motor. Moreover, the deterioration of dynamic performance caused by alterative working conditions can be compensated effectively by the redesign of the control input.