The structural evolution of Cu-12 wt?%Ge (similar to Cu-11 at.%Ge) alloy processed by means of mechanical alloying (MA) with subsequent heat treatment was studied using X-ray diffraction profiles, scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM observations as well as differential thermal analysis(DTA). The fcc Cu(Ge) solid solution (a) was produced at early stages of MA and amorphised upon further milling. This was followed by the formation of xi-Cu5Ge intermetallic nanocrystals after 40 h of milling. The subsequent annealing process led to the nanocrystallisation of the amorphous powder. The X-ray crystallite size data showed the exceptional thermal stability of the alloy prepared. The mechanism of the stability was also investigated. In addition, a thermodynamic analysis based on Miedema's semiempirical model was carried out for the evaluation of the experimental results and a good agreement was found between them.