Polymer Electrolyte Membrane Fuel Cell (PEMFC) stack power output is needed to be approximately 100 kW to meet the requirements of automotive applications. In order to secure the electric safety for drivers, passengers and mechanics, it is very important to understand phenomena of an electric insulation in a fuel cell vehicle. In this study, we studied the electric insulation properties and the insulation resistance of stack, system and vehicle in the field of fuel cell was estimated at the applied voltage of 500 V, respectively. Also we discussed the insulation factors such as the conductivity of coolant, the element of vehicle design and the intrinsic resistance of the vehicle components.