This paper presents a robust controller design based on Q-parameterization theory for the automatic generation control problem of a power system. This controller is used in order to achieve both robust stability and good dynamic performance against the variation of system parameters. In the Q-parameterization method, the set of all stabilizing controllers of the power system is characterized by a free parameter Q. This free parameter is chosen to satisfy robust stability and other design requirements. Simulation results have confirmed the effectiveness of the proposed controller.