Underground miners highly exposed to thermal stress hazard. Closed condition, heavy work load, and limited ventilation are the common cause of high environment temperature in underground mining. Thermal stress can influence metabolism and physiological function of human body. The objective of these study is to investigate the effect of thermal stress to physiological (bodyweight, blood pressure, urine specific gravity, and heartbeat) of underground miners. This study is observational cross sectional study with 42 underground miners. Thermal stress level is 147.14 Wm2 and categorized as unrestricted zone. These study showed that urine specific gravity, blood pressure, and heart beat on underground miners were change after shift work, while the body weight changes were not observed. The relation among TWL with blood pressure, urine specific gravity, and heartbeat is low category.heat conductor from the rocks so that the heat transfer is hampered. Low air transfer and high humidity reduce body ability to release body heat through evaporation.Underground environment having high ambient temperature and heavy work activity could result a health disorder called Heat Related Ilness (HRI), such as dehydration. The research in Australia on underground miners with ambient temperature 36.2°C indicates that 60% miners begin to work in dehydrated condition already. The hazardous exposure of thermal stress could also affect metabolism and physiologic as body adaptation form, like the change of blood pressure, urine specific gravity, body weight and heart beat. Beside, the condition where the thermal stress emerge