Using the computerized energy compensated time‐of‐flight atoms‐probe (AP‐FIM), we have obtained an absolute composition depth profile of a NiCu alloy with single atomic layer spatial resolution. For bulk composition of 3.1%±0.5% Cu at 650°±20°C, the topmost layers of the (111) and (001) planes are enriched to (17%±2.7%) and (36.6%±7.5%) Cu, respectively. Slight depletion of Cu is observed in the near surface layers. Both an irregular solution model and a regular solution model with surface enthalpy relaxation are found to agree semiquantitatively with our results. A comparison with the results from other surface techniques is also made.