A new combined method based on optimal control is proposed to enhance load frequency control dynamics. This method include of PSO and optimal output feedback controller. In the output feedback method only the measurable state variables within each control area is required to use for feedback. The optimal control law is determined by minimizing a performance index under the output feedback conditions leading to a coupled matrix equation. But for more accuracy and better design for this controller, PSO algorithm is applied to find the gain matrix of the controller. The results of the simulation are shown that with using this method, the load frequency control requirements in a practical environment are satisfied and also better dynamic responses are accessible.