Abstract: In order to obtain 2-DOF parallel flexible-structure micro-positioning stage with good static and dynamic characteristics, a new stage configuration is proposed, which is optimized by a size optimization method. The principle and modified morphology of the Stewart parallel mechanism is applied to designing the stage structure, and a new configuration with elastic elements of dual arc thin plates is designed for 2-DOF parallel flexible-structure micro-positioning stage. The stiffness expression in all directions of the stage is given with the deformation theory of curved cantilever beam. And through summating the stiffness expression in all directions, a unified objective function for size optimization of the stage is established by weighted combination approach. Then the mathematical model is solved using sequential quadratic programming (SQP). The static and dynamic characteristics of the stage before and after optimization are tested experimentally. The results show that: the displacements of the optimized stage in x and y directions are 22.98μm and 23.15μm at the driving voltage of 150 V, meeting the design requirements. The natural frequencies of the optimized stage in x, y, z directions are 1.731 kHz, 1.722 kHz and 1.725 kHz. The dynamic characteristics of the optimized stage are more equal in each direction. The response time of the optimized stage in x and y directions at the input step force of 50 N are 18 ms and 20 ms, which are shorter obviously after optimization.