In an interconnected power system, small disturbance occurs in load at each area that causes fluctuate the frequency from its nominal value and also tie-line power flow between different areas are fluctuate. Therefore the main role of load frequency control is to maintain the frequency at nominal value and to keep the net interchange power between pool members at the predetermined values. This can be done by conventional controllers. In this paper, the conventional PI controller is used as a controller in the multi-area interconnected power system. Comparisons between with PI controller and without the PI controller is presented using Matlab/Simulink.