This paper describes an application of nonlinear decentralized robust control (Guo. Jiang & Hill, 1998) to large-scale power systems. Decentralized power controllers are designed explicitly to maintain transient stable closed-loop systems. For the first time, nonlinear bounds of generator interconnections are used which achieves less-conservative control gains. The proposed controllers are robust with regard to uncertain network parameters and attenuate the persistent disturbances in the sense that the L-2-gain from the disturbance to the power frequency is reduced to a certain level. Simulations on a two-generator infinite bus power system exhibit enhancement of system transient stability at different conditions of operation points, fault locations and network parameters.