A micro-/nanopositioning system with both large motion range and compact size is highly desired in various precision engineering applications. In this paper, the design of a new compliant micropositioning stage with translational motion is proposed based on flexure mechanisms. The stage parameters are optimized by using the genetic algorithm (GA) to achieve a large natural frequency under the constraints on motion range (i.e., over 10 mm) and compact physical dimension along with a high safety factor for the material. Both analytical calculations and simulations based on finite element analysis are performed to validate the stage performances. A physical prototype system which employs a voice coil motor and a laser displacement sensor for actuation and sensing, respectively, is fabricated for experimental tests. Result confirms the long-stroke performance of the developed micropositioning system.