A decentralized load frequency controller (LFC) is developed on a two-area interconnected power system with non-reheat turbines only. The nonlinearities such as governor dead band (GDB) and generation rate constraint (GRC) are included in the block diagram of the power system. A sliding mode based LFC is applied to each area of the power system. Our control goal is to regulate frequency error and tie-line power error despite the presences of power load changes and parameter variations. The sliding-mode based LFC is simulated on the nonlinear interconnected power system. The simulation results demonstrate the robustness of the control system against external disturbance and system uncertainties. They also verify the effectiveness of the LFC by driving the frequency error and tie-line power error to zero.