The core conversion from MEU fuel to LEU of the JMTR, a 50 MW light water moderated and cooled tank type reactor using ETR-type fuel, is scheduled in 1993. As a part of the safety analyses for the JMTR LEU core, the neutronics characteristics analysis was carried out. In conversion to LEU fuel, the following things will be changed in JMTR operation: (1) extend the cycle length from 12 days in the present MEU core to 25 days, and (2) introduce cadmium wires with a diameter of 0.3 mm as burnable absorber in the sideplates to reduce the excess reactivity at the beginning of cycle. This report describes the analytical methods and results of the nuclear characteristics analysis of the JMTR LEU core. The results show that the LEU fuel core would provide neutronics characteristics similar to those of the MEU fuel core and the use of Cd burnable absorber is effective for the JMTR operation. (author).