In designing controllers for large-scale systems such as spread power systems, three issues need be considered. Firstly, because there may be lack of global information shared by all substations, large-scale power systems are modelled as interconnections of low order subsystems. Hence, decentralized control becomes a feasible approach. Secondly, because system models are usually approximations to the actual process and because of the uncertainties associated with environmental conditions, robust controllers are desired. Finally, the control strategies must be based solely upon output information, i.e., in many cases, the entire static information is not known. Hence output feedback structures are required in the control strategy. This paper presents a method for designing decentralized robustly stable output feedback controllers for power. system. The approach is based upon a state-space formulation of each subsystem and the associated interconnec-tions. An example of a four-generator, four-load system is presented to illustrate the approach.