[en] Fission products, which were created in a UO₂ matrix during irradiation, depend on burnup, power, average neutron energy, irradiation time and cooling period, etc. According to their physical and chemical characteristics, fission products divide three groups, that is, soluble in UO₂(solid formation), insoluble in UO₂(precipitate) and volatile fission gases. Simfuels(simulated fuel) are fabricated to duplicate an irradiated nuclear fuel. There are abundant studies on some characteristics and fabrication of simfuel due to the non-active material. In this report, three different contents of (U,SS)O₂ pellet were fabricated. SS is a mixture of 7 soluble oxides -SrO, Y₂O₃, ZrO₂, TeO₂, La₂O₃, CeO₂ and Nd₂O₃- in UO₂ matrix. SS-1 have a 1.63wt%, SS-2 have a 3.25wt% and SS-4 have a 6.51wt% of soluble oxides in UO₂ matrix. Steady-state reep strain rate, transition stress, stress exponent and creep activation energy of these contents of (U,SS)O₂ pellets were investigated