The high temperature engineering test reactor (HTTR) is a graphite-moderated and helium gas-cooled reactor with a thermal output of 30MW and a reactor outlet coolant temperature of 950°C during the high temperature test operation. Fuel elements, control rod guide blocks and replaceable reflector blocks are main core components of the HTTR. The core components are mainly made of ceramics, such as graphite, silicon carbide, etc. which are excellent thermal resistant materials.Design requirements for the core components were laid down and extensive design efforts and R&D were performed in order to maintain their structural integrity. The structural integrity of the core components was ascertained by performing evaluations on the basis of the R&D and stress analysis results.This paper describes the design requirements and design details of the core components, and the structural integrity evaluation results for the fuel and graphite blocks.