This paper presents the results of a stability investigation of a power system with longitudinal structure and its stabilization by coordinated power system stabilizers (PSSs). The effects of the existing controllers on system stability are studied. If no PSSs are present, the damping of various swing modes in the system will be very poor and low frequency oscillations present. Eigenvalue analysis shows that the undamped modes are sensitive to excitation control while speed governors have little influence on damping. In order to enhance the overall system stability through excitation control, a coordinated design procedure for power system stabilizers has been developed based on generation coherency, total coupling factor and nonlinear simulation. A PSS designed using this procedure is robust to different operating conditions and very effective for damping oscillations. Comprehensive simulation studies were conducted and results are presented. >