This paper reports the thermal management of a prismatic Li-ion battery pack consisting of a total of 18 cells based on reciprocation flow and active control. Both controlled experiments and accompanying analysis are reported to illustrate the effectiveness of reciprocating cooling flow combined with active control for regulating the cell temperature, reducing temperature non-uniformity, and minimizing parasitic power consumption. Experimentally, a platform with a 3 by 6 prismatic battery module was constructed to perform controlled tests on several competing cooling strategies, including unidirectional cooling flow, reciprocating cooling flow with constant period, and the actively controlled reciprocating cooling flow. The surface and core temperatures of the cells were monitored by the thermocouples during the tests. The major observations from these experiments were twofold. First, the reciprocating cooling flow is effective in reducing the maximum temperature rise and the temperature non-uniformity in the battery pack of practical size. Second, the active control of the reciprocating flow can further reduce both the temperature non-uniformity and the cooling power consumption with a minimal increased maximum temperature rise. Thus through the active control of reciprocating cooling flow, the battery pack can reach a more uniform temperature at the minimum parasitic energy consumption. Published by Elsevier Ltd.