In this study, distributed piezoelectric sensor/actuator systems for the vibration control of the composite plate are designed. A new 2D modal transducer theory is developed based on the finite element modeling of the integrated structure. This theory enables one to determine spatial gain distribution required for the realization of specific modal transducer, without restrictions on the geometry and boundary conditions of the structure. As the practical means for the implementation of optimal gain distribution obtained, two design methods for the distributed modal transducers are developed. First, using multi-layered PVDF film, modal transducers are designed by optimizing electrode patterns, lamination angles, and relative poling directions of each PVDF layer. Second, modal transducers are designed by dividing whole spatial area of a single PVDF film into several electrode segments and optimizing gain-weight on each electrode segment. These two design methods correspond to the approximation of a continuous function using discrete values. For the experimental demonstration, sensors/actuator systems for the control of first and second vibration modes of cantilever composite plate are designed using the proposed methods. Sensors are designed to minimize the observation spillover and actuators are designed based on the criterion of minimizing the system energy in the control modes. The real-time vibration control of integrated smart structures is successfully achieved.