In this paper we describe a two-degree of freedom (T-DOF) configuration of a generalized predictive control (GPC) and an application for an NOx decomposition process of a combined cycle power plant. T-DOF GPC that is designed with feedforward signals, measurable disturbance signals and a reference signal is able to prevent an undesirable action which is caused by the feedforward control. We also describe that the present T-DOF GPC is a similar to the controller with the minimal order observer. We show experimental results accomplished on a commercial power plant.