Uniaxial compression test, Brazilian test and fracture toughness test were carried out for Inada granite and Shirahama sandstone in pure water controlling the water temperature between 0 °C and 80 °C and the loading rate between 1.67 × 10-7 m / s and 5.00 × 10-4 m / s. The uniaxial compressive strength, Poisson's ratio, Indirect tensile strength and stress intensity factor decreased with the temperature for the both two rocks. This tendency was clearer for Inada granite. Critical compressive strain value (axial strain value at peak load point) of Shirahama sandstone also decreased with temperature. However, the effect of temperature on the critical extensile strain (radial strain at peak load point) was not clear for the both two rocks. Young's modulus seemed to take the peak value at 20 °C or 40 °C. These results were explained based on thermal stress due to anisotropy and difference of thermal expansion coefficient between the mineral grains, stress corrosion and change in viscosity of water.
