A novel approach is presented to determine the local burnup in irradiated fuels using isotopic quantification obtained by Atom Probe Tomography (APT). Considering the volume of sample used (<100 mm3) for APT experiments using the lift-out process in a scanning electron microscope equipped with a Focused Ion Beam (FIB), the presented method determines the local burnup from a nuclear fuel, where a minimal amount of waste is produced. In this work, three samples were analyzed with different burnup conditions: as received low enriched 19.8% U-235, intermediate burnup (~52% U-235 fissioned) and high burnup (~69% U-235 fissioned) UeMo fuel. APT is used to quantify the isotopes of 235U, 236U, 238U, 239Pu and 237Np for burnup calculation in the irradiated metallic Ue7Mo dispersion fuel. The equation used to estimate the burnup of fuels is derived by considering that the initial counts of U is equal to the sum of remaining atoms of U isotopes and all the U reactions undergone during irradiation. This method provides U enrichment and local burnup with an unprecedented high spatial resolution based on quantification of isotopic ratios of U.