The recent advances in waste heat recovery technologies have provided great opportunities for energy conversion efficiency improvement. This paper proposed a metal foam filled thermoelectric generator (TEG) for the utilization of liquid waste heat resource. A prototype was designed and constructed to study the performance enhancement due to metal foam inserts. High-temperature oil based experiment was conducted to investigate the TEG performance in higher liquid temperature. The influences of hot oil inlet temperature and cold water flow rate were proved to be key operating parameters for the TEG performance. Specially, net power output and net power enhancement ratio were presented to assess the overall net power output performance. The metal foam filled TEG was demonstrated to outperform the unfilled TEG both in power generation efficiency and net power performance. In the experiments, the maximum power generation efficiency and net power enhancement ratio of metal foam inserted TEG were 2.49% and 1.33, respectively.