Active damping control of the structural vibration of a one-dimensional cantilever plate is analyzed and tested. The control algorithm employs rate feedback without using any element tuned to the structural vibration frequencies, so that the senstivity of the closed-loop stability and performance to resonant frequency variations are minimized. PVF2 layers were attached to all sides of three steel plates to act as distributed actuators and sensors. Both all-mode and single-mode actuator/sensor pairs were designed and studied, and experimental results showed that critical active damping control for the first mode was achieved. The importance of having a distributed modal actuator/sensor for the active damping control of a flexible structure is established.