Fuel cells are eco-friendly energy devices with high efficiency. They are regarded as ideal power sources, especially for hybrid vehicles with rechargeable batteries. In this study, we proposed the parameters for the optimal hybrid ratio of a fuel cell hybrid electric vehicle (FCHEV). We made a model FCHEV with fuel cells and rechargeable batteries (Li-ion batteries) and carried out various tests to obtain parameters for several driving conditions. These parameters are used to find the optimal ratio of the power of the fuel cells to the total power (power of fuel cells + power of rechargeable batteries). The results indicate that the optimal hybrid ratio is 0.4. In this case, the powers from the fuel cells and rechargeable batteries are about 50 and 70 kW, respectively. The optimal parameters in this study can be used to develop power transmission systems of FCHEVs. The results of this study are expected to improve FCHEVs to become an important means of mass transportation.