In the past two decades, conventional power system stabilizer (PSS) is widely used to damp power systems oscillations. Nowadays, several approaches based on intelligent techniques have been applied to PSS design problem. This paper deals with optimal design of multimachine power system stabilizers to improve the dynamic stability of power system. The design problem is formulated as an optimization problem. Non-Dominated Sorting Genetic Algorithm (NSGA-II) is employed to search the optimal PSS parameters‥ Based on a three-machine nine-bus test system, nonlinear simulation results under disturbance, show the effectiveness of the proposed approach in power oscillation damping.