In our recent papers, we presented a new technique for determining the thermal shock fracture toughness, using a disk specimen with an edge crack.The thermal shock fracture toughness is defined as KICk/Eα (KIC standing for fracture toughness;k for thermal conductivity;E for Young's modulus;α for thermal expansion coefficient) and it can be determined en bloc by measuring the threshold electric power of the arc discharge heating produced when an edge crack propagates in the disk.The value obtained is the fracture toughness corresponding to the thermal shock resistance defined as σ k/Eα (σ standing for tensile strength).The experimental data shown in the following discussion concern themselves with four kinds of reactor grade graphite and some varieties of electrode graphite.