Hybrid electric vehicles powered by fuel cells have been focused for alternative powertrains due to their high efficiency and low emission. The relative engine sizing and power split strategy of different power sources have great effect in influencing the fuel economy. In this paper, for a given driving cycle, the overall efficiency of a fuel cell/battery hybrid vehicle is maximized by identifying the best degree of hybridization (DOH) and a power control strategy. Fuzzy logic is used in power distribution of the hybrid vehicle, where the optimized centers and widths of membership functions are found by optimization. Simulation results show that the optimally designed and controlled hybrid vehicle can provide good fuel economy and overall system efficiency.