A piezoelectric actuator using bridge-type flexure hinge mechanisms is developed and optimized to amplify the displacement of a multilayer piezostack. The developed hinge mechanism has three-dimensional structure to reduce its size, so it has a high amplification ratio in a relatively small size. The developed mechanisms are modeled by matrix methods assuming flexure hinges as 6 degree-of-freedom spring elements to show the validity of the proposed hinge mechanism. To verify the derived matrix model, displacement and frequency experiments are performed. The experimental result shows that the displacemental error between the matrix model and experiments is below 10%. This indicates that the deformation of the hinge in the parasitic direction should be considered for more exact estimation of the amplification of the bridge-type hinge mechanism. Using the developed matrix model, an optimization is performed to estimate the performance of the hinge mechanism. (C) 2004 Elsevier B.V. All rights reserved.