In this paper, a digital regulator is designed and experimentally implemented for a smart structure featuring piezoelectric sensors and actuators using optimal multivariable control techniques. The controller consists of a linear quadratic regulator with output weightings and a state estimator, Luenberger observer. The structure is a cantilever beam synthesized with two sets of sensor/actuator PZT ceramic piezoelectric plates bonded to the beam surface at the high strain locations corresponding to the first and second vibration modes. Equations of motion of the beam are developed using finite beam element model. The model includes the mass and rigidity of the PZT ceramics. Experimental results of two regulators differing in the number of modes considered are presented and discussed. The results proved the applicability of the concept and the stability and robustness of the control algorithm.