The nanostructured phases formed in the elemental powder blends of nominal compositions Al 92 Mn 6 Ce 2 and Al 93 Mn 6 Ce 1 during mechanical alloying were investigated by X-ray diffraction and transmission electron microscopy. The difference in Ce content in the two alloys strongly influenced the types of the intermetallic phase(s) formation, including those of the Ce-free phases. Partial amorphization observed in Al 92 Mn 6 Ce 2 after prolonged (60 h) milling was not apparent in the lower Ce bearing alloy. Analysis of the X-ray diffraction data of these alloys along with those reported in the literature indicated the dominant role of the topological factors in the amorphous phase formation by mechanical alloying of the concerned system. The phases present in the mechanically alloyed Al 92 Mn 6 Ce 2 were entirely different from those reported for rapid solidification processing of the same composition [A. Inoue, Nanostruct. Mater. 6 (1995) 53-64.]. Moreover, the phases present in the mechanically alloyed powder showed inferior thermal stability, when compared to that reported for the rapidly solidified product, apparently due to the difference in the nature of structural disorders and strain induced in the products by the two non-equilibrium processing routes.