Abstract: Optimal synthesis procedure of a planar 3-DOF 4RRR overactuated parallel mechanism is investigated to design a full-compliant multi-degree-of-freedom overactuated parallel mechanism.Firstly,the kinematic models are developed for the general 3-DOF four-limbed planar parallel mechanism.Then,the possible topologies of the mechanism are classified into four categories,and their kinematic and dynamic performances are analyzed and compared.A global optimization model for the parallel mechanism is established to improve its manipulability,and a numerical optimization example using genetic algorithm is presented.Based on the numerical result,a planar 3-DOF full-compliant overactuated mechanism is designed and fabricated.The optimal synthesis procedure can be applied to other full-compliant mechanisms.