This paper proposes a decentralized output feedback control scheme for the multi-machine power system. The synthesis problem is formulated as scaled H_∞ control problem and a novel LMI-based algorithm is developed to compute the decentralized output feedback controller. The proposed control law provides robustness with regard to parametric uncertainties and attenuates bounded exogenous disturbances in the sense of L₂-gain. Simulation results clearly show the effectiveness of the proposed decentralized robust output feedback control scheme.