The kinetics of intermediate phase formation in the Cu/Mg multilayer system is analyzed using Differential Scanning Calorimetry. Three main exothermic processes are found during the continuous DSC treatments. The first two, significantly overlapped, are related to the same process, nucleation and growth of the Mg2Cu along the interface. We interpret differences between the Mg/Cu and Cu/Mg interfaces are at the origin of this unexpected behavior. The third exothermic reaction is due to the growth of the Mg2Cu phase perpendicular to the original interface. A kinetic model is developed which yields calorimetric traces in good agreement with the experimental data.