Geothermal energy piles (GEP) are a renewable energy technology that have been used as a cooling and heating source of building air-conditioning system. Brazil is currently the fifth largest buyer of air conditioner in the world, mainly due its tropical and subtropical climate, and the use GEP could be an interesting alternative to reduce the consumption of electrical energy for air-cooling systems. For an accurate design of energy foundations it is essential to estimate the ground thermal properties. However, the thermal properties of unsaturated tropical soils, that cover a significant part of the Brazilian territory, were not investigated before. These soils are products of weathering processes in tropical warm and humid climates, and generally present high contents of aluminum and iron oxides. To address that need, the current work was carried out to investigate the thermal properties of Brazilian unsaturated weathered soils of two different sites. For this study, thermal needle probe tests were performed on disturbed and undisturbed samples of tropical soils, and on silica sand under different moisture conditions for comparison. The results indicate that the particular mineralogical composition of the tropical soils investigated and the soil moisture content of sand have influence on soil thermal properties.