The aim of this research is to study passive coolingfrom earth contact surface. The temperature of humid soilwill nearly to the temperature of wet pulb which made theenvelope of building contact surface cool. This method willsave energy. Building user can set room temperature higherfor expanding thermal comfort range wider. To passively cool the building from earth contactsurface, the ground condition has to be studied first whichdifference of selected ground is ordinary ground that can beseen anywhere. An 8x8 m. building is constructed to haveinsulated walls, ceiling and roof to provide extraprotection against the heat from the roof. Then, thevariables affecting gound temperature are studied. Theseare ground depth, ground condition, soil which convered bysmall plants and influence to building's aspectus.Temperature is taken every hour. Data are collected for 2-3consecutive days from December 1995 to February 1996. The data are finally analyzed. Findings : The groundtemperature is rather stable, range of temperature is2-3 degree C . The highest range of temperature in 24 hoursis on the south. The lowest range of temperature in 24 hoursis on the north. Ground condition covered by small plantswill cooler than naked ground 2 degree C. The temperatureinside builing at level 1.5 meter from floor will decreaseand change against air temperature which is anytime airtemperature high temperature inside will low and if airtemperature cool, temperature inside will warm (24-26.5degree C) caused by influence of ground time lag. After thisresearch finds time lag is 10-12 hours. This research finds reduced temperature 1.5-2 degreeC, inside temperature rather stable and buildingtemperature is a comfort temperature. If the buildinghas not air-condition, the result of passive cooling willdecrease MRT in the building. That made user feel cool. Ifthe building has air-condition, the result of passivecooling will decrease energy load. The findings can beapplied to future design and land scape architecture.