A solution region design method based on planar sixbar mechanisms for robotic fingers was proposed to achieve the goal of obtaining diversified fingers with different dimensions. An infinite number of solutions of planar sixbar mechanisms can be obtained by predefining four moving positions, and all these solutions can be expressed on a planar region, which was called the solution region. Firstly, the planar sixbar mechanisms had five moving links, and three of them simulated the proximal, middle and the distal knuckle of human fingers, respectively. Four moving positions of the three links, which expressed the bending motion of a finger, were predefined. The coordinates of unknown joints, which were located inside the finger, were limited to restrict them in the kunckle. According to the theory of motion generation in four moving positions of planar sixbar mechanisms, the solution curves and feasible segments of the known joints were obtained. After segmenting the feasible segments, a solution region of planar sixbar mechanisms, expressed by the coordinates of two joints, was established. The parameter K, an index that measured the force transmission property of a mechanism, was introduced to filter the feasible segments. Then a feasible solution region was obtained, and the distribution law of K on the feasible solution region was analyzed. Finally, A planar sixbar mechanism was selected on the feasible solution region to design a finger prototype. The new feasible solution region expressed actual coordinates of the joints, and showed the force transmission property of planer sixbar mechanisms directly, which contributed to the selection of mechanisms that satisfied all the requirements. Each point on the feasible solution region was a planar sixbar mechanism. Therefore, appropriate planar sixbar mechanisms can be selected on the solution region according to different design objectives, such as anthropomorphic fingers, rehabitation fingers. And the prototype proved the validity and availability of the solution region design method for robotic fingers design.