This paper proposes a modified version of real immune algorithm (RIA) using population management, namely, RIAPM, to simultaneous coordinated tuning of power system stabilizers (PSSs) in a power system. A conventional lead-lag structure is considered for the controllers. Since, the parameters of leadlag controllers are continuous variables to be found and an infinite number of candidate solutions will exist, therefore a modification will be considered to RIA to reduce the search space gradually, in order to get a more detailed investigation in a smaller region. Using the RIAPM, the parameters of the damping controllers are optimized simultaneously and the interactions among the controllers are considered. The numerical results are presented on a 2-area 4-machine system to illustrate the feasibility of the proposed method. To show the effectiveness of the designed controllers, a three-phase fault is applied at a bus. The simulation study shows that the RIAPM performs better than RIA. (C) 2009 Elsevier Ltd. All rights reserved.