Lead-cooled Fast Reactors (LFRs) with mixed-oxide (MOX) fuel are promising candidates in the Generation IV (Gen IV) small modular reactor (SMR) landscape due to their capacity for actinides transmutation, passive safety features, and minimized waste radiotoxicity. For secure management, storage, safeguards, rigorous characterization is necessary. This database was developed to support the optioneering and design of MOX-based lead-cooled fast reactors. This data article introduces a comprehensive dataset of isotopic mass densities, spanning 152 nuclides present in irradiated LFR-MOX fuel, additionally providing insights into fuel characteristics such as activity, decay heat rates, photon emission rates, spontaneous fission rates, and radiotoxicity values across various decay steps. Using the Serpent2 Monte Carlo code for fuel depletion calculations, and processed with SerpentTools, the dataset captures inventory data as a function of reactor power, fuel burnup, plutonium vector in the fresh MOX, and decay time at the end of irradiation, enabling analyses of SNF properties. The dataset is stored in Parquet format, including one primary depletion file and 13 decay files.