Because of the environmental issues, hybrid/electric vehicles are becoming the focus of the automotive industry and research field. From this trend, permanent magnet (PM) motors are receiving much attention because hybrid/electric vehicles can replace internal combustion engine as a PM motor to generate driving force. Like internal combustion engine, PM motor can produce power and also heat losses during the driving mode. So PM motor need cooling system to maintain the temperature lower than the temperature limit. So minimizing power consumption for the cooling system can directly affect the mileage extension of electric vehicle. So in this paper, optimal operation control of motor cooling system is studied based on the thermal characteristics of PM motor. For the optimizing PM motor cooling system, thermal modeling of PM motor is also conducted. If heat losses and heat transfer characteristics of PM motor are considered, cooling system control can be conducted efficiently. From the saving power of the cooling system, mileage extension of electric vehicle is calculated for the given driving mode. If the algorithm of the cooling system control is applied for another system of electric vehicle like battery or any other electrical component, electric vehicle driving range will be extended or battery size can be minimized.