It is well known that internal combustion engines have approximately 30% thermal efficiency, and the remaining energy is lost as heat through both, exhaust gas and coolant. To improve upon this efficiency, technology for recycling waste energy is desirable. Increasing the thermal efficiency of engines would also reduce CO2 emissions. Recently, waste energy recovery systems have drawn-a great deal of attention for their potential ability to address stringent emission regulations as well as fossil fuel depletion. Thermoelectric generators (TEGs) can be applied to produce electricity from waste heat; however, there are still remaining many problems to be solved. It would be significant not only to improve the efficiency of the TEG, but also to optimize the operating conditions. Therefore, this study provides useful information on optimization of the TEG system, including optimization of the system layout, and configuration Of TEG. In addition, the heat transfer characteristics of thermoelectric modules were predicted by theoretical analysis and compared to experimentally measured heat transfer characteristics. The performance of thermoelectric generators heated by exhaust gas from an actual engine was investigated. From these results, we clarified factors affecting the optimization of thermoelectric module according to operating conditions. (C) 2015 Elsevier Ltd. All rights reserved.