ABSTRACTFissile fuel breeding in the ARIES-ST of the 1000 MWel power plant is investigated by using molten salt containing UF4 Calculations are done with the aid of one-dimensional code of SCALE4.3. In this hybrid model, a substantial amount of fissile fuel can be produced with a fissile fuel breeding ratio of 239 Pu = 0.115 per incident neutron at start-up conditions, that corresponds to 3558 kg 239 Pu/year by a full fusion power of 2740 MW. Tritium breeding ratio is found as 1.14 so that tritium self-sufficiency is maintained for DT fusion driver.  Key Words: ARIES-ST fusion reactor, molten salt, fissile fuel breeding.