In this study, the topology optimization is applied to the design of a piezoelectric microactuator satisfying the specific mean transduction ratio(MTR). The optimization problem is formulated to minimize the difference between the specified and the current mean transduction ratio. In order to analyze the response of the piezoelectric-structure coupled system, both the structural and the electric potential are considered in the finite element method. The optimization problem is resolved by using Sequential Linear Programming(SLP) and the results of test problems show that the design of a piezoelectric microactuator with the specified mean transduction ratio can be obtained.