A nonlinear variable structure stabilxzer is proposed in this paper. Design of this strabilizer involves the nonlinear transformation technique, the variable structure control technique and the linear syste theory. Performance of the proposed nonlinear variable structure controller in a single machine connected to an infinite bus power system and a multi-machine system with multi-mode oscillations is simulated. The responses of the system with the proposed stabilizwer are compared with those obtained with some other kinds ofstabilizers wthen the systemis subjected to a variety of disurbances. Simulation results show that the nonlinear variable structure stabilizer gives satisfactory dynamic performance and good robustness.