A novel liquid cooling device for a prismatic LiFePO4 battery module was proposed and manufactured in this study in order to improve the thermal management performance of the battery module operating at high ambient temperature.A testing system was set up to experimentally measure temperatures in different locations of the battery module consisting of seven 60 Ah cells.Tests were conducted to investigate both the passive and active cooling performances of the proposed system at different ambient temperatures and discharging rates in regarding with the maximum temperature and difference between the maximum and minimum temperatures.The results clearly show that both the ambient temperature and discharging rate play important role on the maximum temperature of the battery module.Passive cooling cannot meet the cooling requirement of the battery module particularly at high ambient temperature of 40℃.In contrary,liquid cooling can successfully reduce the maximum temperature to the required temperature range of the battery module even in high temperature environment and relatively high discharging rate.The effect of water inlet temperature on the cooling performance was also experimentally studied.With the inlet temperature of 28℃,the active cooling device can reduce the maximum temperature of the battery module to about 34.8℃ after discharging at 0.6℃ for 1000 s.The temperature difference of only 3.8℃ was also achieved which suggests a great uniform distribution of temperature in the battery module.