The HTTR (high-temperature engineering test reactor) fuel, the first mass-produced HTGR (high-temperature gas-cooled reactor) fuel in Japan, has been fabricated with high quality on the basis of design principle and safety criteria to minimize both as-fabricated failure and on-operating-additional failure of the coated fuel particle. A precise technology for evaluating irradiation performance of the HTTR fuel has been developed by measuring fission gas released from the fuel and constructing the fission gas release model. Through the HTTR operations, including the continuous high-temperature operation at 950 degrees C for 50days, the measured fractional release of fission gas from the fuel was less than 1.2x10(-8), and a superior irradiation performance of Japanese HTGR fuel has been demonstrated. The HTTR fuel technologies could make a prospect for realization of the VHTR (very high temperature reactor) as a Generation IV nuclear power plant as well as the practical HTGR for the first time. This paper describes the fuel performance under continuous high-temperature operation of the HTTR.