The objective of this study was to investigate heating performance characteristics of coolant heat-sourced heat pump system in a fuel cell electric vehicle (FCEV). In order to analyse heating performance characteristics of heat pump system with triple fluids heat exchanger between stack cooling coolant and a refrigerant, R-134a, each component in the heat pump system was installed and tested under various operating conditions, such as air inlet temperature of HVAC system and compressor speed. Heating performance of tested system was studied with respect to heating capacity and COP (Coefficient of Performance) after various experiments according to FCEV driving conditions. Because tested system had EXV (Electric Expansion Valve) to control the refrigerant mass flow rate, heating performance was analysed along with EEV opening under certain conditions, such as inlet air temperature and compressor speed. When the air inlet temperature of HVAC system was varied from 0.0℃ to –20.0℃, heating capacity was found to be similar due to somewhat equal temperature difference between inlet and outlet of HVAC system. However, COP increased until certain EEV opening, especially under 45.0%, because of decreasing electric compressor's power consumption. When the compressor speed was varied from 2,000 to 4,000 RPM, while heating capacity increased, COP decreased by higher refrigerant mass flow rate. In the future works, performance characteristics according to stack cooling coolant's operating conditions, such as temperature, coolant volume flow rate, would be analysed with respect to heating capacity, system efficiency, and triple fluid heat exchanger's pressure drop.