A method of measuring impedance of a fuel cell stack in a vehicle during driving of the vehicle includes: determining whether an impedance measurement of the fuel cell stack is requested during driving of the vehicle driven by power of the fuel cell stack; turning off a first relay connected between the fuel cell stack and a battery charged by the fuel cell stack when the impedance measurement of the fuel cell stack is requested; connecting a stack load to the fuel cell stack via a second relay and supplying air to the fuel cell stack; and measuring the impedance of the fuel cell stack.