[en] Preliminary studies on Burnup Credit for PWR MOX fuels have pointed out the difficulties related to the determination of a conservative isotopic composition to cover a wide range of MOX fuels. Indeed, contrary to PWR UOX fuels, for PWR MOX fuels, a fresh-fuel conservative isotopic composition does not inevitably lead to the most reactive situation after irradiation due to the amount of plutonium fertile isotopes (²³⁸Pu, ²⁴⁰Pu...). Latest studies related to the use of Burnup Credit for PWR MOX fuels have shown that the fission products contribute to the reactivity decrease more significantly than the actinides for a cooling time of up to 5 years. This observation allows to consider an implementation of Burnup Credit for PWR MOX fuels based on the reactivity worth of only 15 fission products (already identified for PWR UOX credit burnup applications): ⁹⁵Mo, ⁹⁹Tc, ¹⁰¹Ru, ¹⁰³Rh, ¹⁰⁹Ag, ¹³³Cs, ¹⁴³Nd, ¹⁴⁵Nd, ¹⁴⁷Sm, ¹⁴⁹Sm, ¹⁵⁰Sm, ¹⁵¹Sm, ¹⁵²Sm, ¹⁵³Eu and ¹⁵⁵Gd. Several calculations were performed to assess the impact of several irradiation parameters on the reactivity worth of fission products (e.g. environment of MOX fuel assembly, control rods insertion, moderator density, fuel temperature, specific power, cooling time). Moreover, further calculations were performed to verify that taking into account a fresh-fuel conservative isotopic composition leads to the most reactive situation after irradiation when Burnup Credit is based only on the reactivity worth of fission products. The objective of the paper is to present the studies allowing to validate a methodology of Burnup Credit for MOX PWR fuels and to estimate the reactivity gain for a configuration of industrial interest. (authors)