The evaluation of the temperature distribution in the mantle from geomagnetic, geoelectric, and magnetotelluric data requires detailed information on the electrical conductivity of the constituent minerals. In addition, electrical properties of minerals and rocks are used in studies of electronic and ionic transport processes, defect chemistry, and other mineral physical properties. Until now, accurate measurements of electrical conductivity at high pressure and high temperature have been difficult. We are attempting to overcome the previous experimental difficulties by reducing leakage current caused by pressure medium, lead wires, and reaction products (between pressure medium and sample), and to control oxygen fugacity. The aim is to measure the electrical conductivity of Earth's minerals and rocks in the multianvil apparatus up to 25 GPa and 1600°C under controlled conditions. We will determine the mantle geotherm by using the laboratory conductivity data of the most abundant mantle minerals and rocks, including olivine ( ), modified spinel ( ), spinel( ), perovskite, and peridotite.