The Japan Materials Testing Reactor (JMTR) is capable of a wide variety of irradiations under controlled environmental conditions. The JMTR has been used to perform engineering tests on nuclear fuels and components, for general materials testing, and for radioisotope production since 1970. The JMTR was operated for approximately 3.5 cycles in fiscal 1993, and extensive irradiation tests including power ramping tests were performed. The development of the latest irradiation and post irradiation examination (PIE) technology, such as the double instrumentation technique of thermocouple and fission gas pressure gauge to an irradiated fuel and the PIE technique of small test piece with destructive inspection, is being carried out in the JMTR. The investigation of irradiation behaviors for the blanket materials in the fusion reactor is also being carried out. The core conversion to low-enrichment uranium (LEU) fuel in the JMTR was fully completed in January 1994. (author).