The structural changes upon milling and subsequent annealing of a Mn54Al43C3 alloy containing the intermetallic tetragonal L10 MnAl phase (¦Ó phase) as the major phase were investigated by X-ray diffraction and atom probe tomography. The analyses show that milling the starting powder for 10 h leads to the nanostructuration of the sample. The milled sample is partly oxidised and contains both non oxidised Mn60¡À5Al40¡À5 regions and oxidised regions. Annealing the powder for 1 h at 500 ¡ãC leads to enrichment in Al of the oxidised regions, and to the phase transformation of the non-oxidised regions into a nanostructured ¦Â-Mn-like phase with a composition close to Mn3Al2.