The geothermal research has been carried out on the Heunghae, Pohang geothermal area know as having geo-heat-flow area in the Korean peninsula. This study results so far indicate that geothermal water in the area is in peripheral waters of hydrothermal area and is not in equilibrium with the reservoir rock. The average oxygen and hydrogen stable isotope values are as follows: deep groundwater $(average:;{delta}^{18}O=-10.1\%_{circ},;{delta}D=-65.8\%_{circ})$, intermediate groundwater (average: $(average:;{delta}^{18}O=-8.9\%_{circ},;{delta}D=-59.6\%_{circ})$, shallow groundwater $(average:;{delta}^{18}O=-8.0\%_{circ},;{delta}D=-53.6\%_{circ})$, surface water $(average:;{delta}^{18}O=-7.9\%_{circ},;{delta}D=-53.3\%_{circ})$ respectively. Deep groundwaters was originated from a local meteoric water recharged from distant, topographically high mountain region and not affected by the sea water. High temperature zone inferred from water geothermometers is around D-1, D-5, D-6, 1-04 well zones. The estimated enthalpy from Silica-enthalpy mixing model is near 410 kJ/kg, which corresponds to the temperature of $98^{circ}C$, and in consistent with the result of Na-K and K-Mg geothermometer.