This thesis presents design of fuzzy proportional integral derivative load frequency control for multi-area power systems using particle swarm optimization. Area-1, area-2, and area-3 comprises Tana Beles, Fincha, and Tekeze hydropower plants respectively. The particle swarm optimization algorithm had been employed to optimize the scaling factors of fuzzy proportional integral derivative (FPID) controller for minimization of system frequency deviation and tie-line power change during load perturbations using integral time absolute error (ITAE) as the objective function. The proposed system had been built in MATLAB/Simulink software. A comparison of PID, FPID, and PSO FPID controllers had been performed under different values of load disturbances and parameter variations. When 0.01 p.u load perturbation was applied to area-1, PSO FPID controller has 14.45 second settling time, 0.00024 p.u peak overshoot, and -0.0057 p.u peak undershoot values. These values indicate that the proposed controller has a better response compared to PID and FPID controllers. On the other hand, when load disturbances of 0.167 p.u in area-1, 0.05 p.u in area-2, and 0.01 p.u in area-3 had been applied, the proposed controller also gave better responses. Robustness analysis had been also checked by applying 0.01 p.u load increment in area-1 and variation for selected power system parameters from nominal values. The frequency and power deviation versus time responses verify that the PSO FPID controller has a shorter settling time, lower oscillation, lower peak overshoot, and undershoot when compared with PID and FPID controllers. These implies the robustness of the designed controller, which enables system frequency to restore its nominal value in a shorter time. Key words: Fuzzy Proportional Integral Derivative, Hydropower, Integral Time Absolute Error, Load Frequency Control, Particle Swarm Optimization.