Today’s modern soldier relies on a dozen electronic gadgets, from standard gear, such as radios, GPS units, and night-vision goggles, to improvised explosive device (IED) jamming system and mine detecting device, all requiring electrical power, for successful mission. In a typical 72 hour mission, requiring average power of 20 W, a soldier carries 70 individual batteries corresponding to 12.7 kg of rechargeable military batteries or 8.2 kg of primary batteries. Batteries account for 20% of the weight a soldier carries in battlefield. To unburden the soldiers by lightening the battery load, thermoelectric generator (TEG) can be a good candidate as a military portable power sources because it has the inherent advantages of quiet operation, few moving parts, and compact and lightweight construction. Particularly, thermoelectric systems can be easily designed to operate small heat sources and small temperature differences regardless of soldier’s mission time and climate change. In this study, we developed a military portable TEG with a maximum output power of 10 W and a weight of 1.2 kg at a designed temperature difference of 140°C. A TEG is composed of four Bi-Te thermoelectric modules (TEMs) connected in series and water cooling. A variety of environmental tests were carried out to investigate the robustness of TEG under the environmental conditions simulated deployment of military soldier use, which were categorized into high temperature (storage, operation), low temperature (storage, operation), humidity, vibration, shock, and transit drop according to MIL-STD-810F. A developed TEG exhibited a reliable electrical performance and no mechanical damage after all of environmental tests. This durability test data of TEG can provide good environmental test criteria in designing the robust TEG as a military portable power sources.