Usually, the membership functions and control rules of fuzzy logic controller are determined by trial and error which is cumbersome and time consuming. Therefore, to surmount such a drawback, this paper makes use of the Genetic Algorithm (GA) technique for optimal tuning of the parameters of the Fuzzy Logic Controller (FLC) used for the switching of the thyristor controlled braking resistor to improve power system transient stability. Following a major disturbance in electric power systems, variable rotor speed of the synchronous generator is measured, and then the current through the braking resistor is controlled by the firing-angle of the thyristor switch which is controlled by the fuzzy logic. Thus, the braking resistor controls the accelerating power in generators and makes the system transiently stable. Through the simulation results, the effectiveness of the proposed technique is confirmed.