A general method is developed of designing distributed modal transducers, especially for use in the active vibration control of structure. For this purpose, a new two-dimensional modal transducer theory has been developed. This theory is based on the finite element model of the structure, which makes it possible to determine spatial gain distribution of the specific modal transducer without restrictions on the geometry and boundary conditions of the structure. Although the optimal gain distribution can he obtained theoretically, there is no practical means of implementing it. Therefore, two design methods of distributed modal transducer are developed, which optimize available parameters of piezoelectric film to approximate optimal gain distribution best. The first method uses multilayered polyvinylidene fluoride (PVDF) films as a single transducer. The electrode pattern, the lamination angle, and the relative poling direction of each PVDF layer are optimized to obtain the desired transducer. In the second method, the whole electrode area on a single PVDF film is divided into several segments, and the gain weight imposed on each segment by interface circuit is optimized. Sensor/actuator systems for the vibration control of cantilever composite plate are designed using the proposed methods. The performance of the designed transducers is verified experimentally. The real-time vibration control of integrated smart structure has been successfully achieved.