This paper presents the design, analysis and testing of a novel three-degree-of-freedom (3-DOF) compliant parallel-kinematic active constant-force stage. The active constant-force property enables a large travel and constant driving property, which is enabled by introducing symmetrical bistable flexure hinges. The folded flexure mechanism is adopted to guide the driving input and to balance the stiffness of the stage to zero. In addition, leaf flexure hinges are employed to decouple the cross-axis motion of the 3-DOF parallel stage. Analytical modeling is conducted to evaluate the stage performance. To verify the performance of the constant-force property and motion decoupling, finite-element analysis simulation study is carried out. By minimizing the fluctuation of the constant-force value, design optimization of the stage parameters is implemented with multi-objective genetic algorithm. Moreover, a prototype is fabricated for demonstration of the proposed concept design.