The core graphite material used for the core graphite components such as fuel blocks, control rod blocks etc. of High Temperature Engineering Test Reactor (HTTR) is nuclear grade fine-grained isotropic graphite (IG-110). The material data on properties such as tensile strength, compressive strength, Young`s modulus, thermal expansion etc., including the effect of irradiation on these properties have been acquired up to now. From these obtained data the design data were stipulated by the graphite structural design code for core graphite components of HTTR in order to design the core graphite structures. This report explicates these design data for the core graphite components of the HTTR. (author).