A method of designing reduced-order robust controllers for smart structural systems, which guarantees the stability and performance of the closed-loop system under various uncertainties, is presented. The uncertainties in structural systems are modeled as norm-bound unstructured uncertainty and structured parametric uncertainties in natural frequencies and damping ratios. Based on the linear matrix inequalities (LMIs) and the Popov criterion, a robust multi-objective controller is designed to suppress the vibrations caused by external disturbances. The limited actuator inputs are also incorporated in the design mythologies. Using LMIs, the order of the synthesized controller is reduced by a frequency-weighted model reduction method. The design procedure was experimentally tested on a multi-input and multi-output three-mass structural test article, which uses piezoelectric actuators and sensors.