According to the development plan for the Korea Space Launch Vehicle, a performance verification satellite will be installed in the launch vehicle in 2021. In addition, three payloads, including a small electrically heated thermoelectric generator (ETG), will be developed and installed in the satellite. In particular, a small ETG has been developed by the Korea Atomic Energy Research Institute for the purpose of evaluating the characteristics of the ETG in the space environment prior to the development of a radioisotope thermoelectric generator for lunar missions. In this study, shock and vibration tests were carried out to check whether the ETG can endure the launch environment of the spacecraft. In addition, a thermal cycle test and a thermal vacuum test were conducted to check whether the ETG maintains its performance, even at drastic temperature changes, which can be applied to the ETG in space. Finally, a periodic performance test was carried out to measure the degradation level of the small ETG.