The DARWIN package, developed by the CEA and its French partners (AREVA and EDF), provides the parameters required for fuel cycle applications: fuel inventory; decay heat; activity; neutron, gamma, alpha, and beta sources and spectra; and radiotoxicity. This paper presents the DARWIN2.3 experimental validation for fuel inventory and decay heat calculations on pressurized water reactors (PWRs). To validate this code system for spent fuel inventory, a large program has been undertaken, based on spent fuel chemical assays. This paper deals with the experimental validation of DARWIN2.3 for PWR uranium oxide and mixed oxide (MOX) fuel inventory calculation, focused on the isotopes involved in burnup credit applications and decay heat computations. The calculation-to-experiment ratio [(C - E)/1] discrepancies are calculated with the latest European evaluation file JEFF-3.1.1 associated with the Santamarina-Hfaiedh energy mesh. An overview of the tendencies is obtained on a complete range of burnup from 10 to 85 GWd/tonne (10 to 60 GWd/tonne for MOX fuel). The experimental validation of the DARWIN2.3 package for decay heat calculation is performed using calorimetric measurements carried out at the Swedish interim spent fuel storage facility, Clab, for PWR assemblies, covering large burnup (20 to 50 GWd/tonne) and cooling time (10 to 30 year) ranges.