This study was conducted to estimate the optimum temperature and required time for soil sterilization when heated water was circulated through underground heating pipes in the greenhouse which solar heat was influenced to the temperature of soil during the summer day. Two different types of heating pipes were used for the experiment. One was a polyethylene pipe(XL) and the other was a corrugated ring shaped stainless steel pipe(STS). The results of the studies were summarized as follows; By measuring the thermal characteristics of the XL and STS, it was examined that the average temperature differences of the inlet and outlet were $8.5^{circ}C$ and $13.3^{circ}C$, the average flowrates were 15.3 L/min and 5.6 L/min, and the average radiation powers were 9.1 kW and 4.1 kW, respectively. As results of the regression analysis of underground temperatures, when average soil temperature was$35^{circ}C$, an average water temperature was $80^{circ}C$, and XL was used, it was estimated that the possible heat transfer distance, the required time for heat transfer and heat flux to reach the underground temperature of $60^{circ}C$ were 300 mm, 230 hours, and $7.57kW/m^2$, respectively.