Single crystals of an Al‐Mn superlattice have been grown by molecular‐beam epitaxy. For thicknesses less than the critical thicknessdc&bartil;30 A˚, Mn atoms form the fcc lattice in the [111] direction of an Al surface grown on sapphire‐C substrate. The modulated structure of the Mn surface has been observedinsituby reflection high‐energy electron diffraction. On the other hand, for thicknesses more thandc, Mn grows in the [110] direction of the bcc lattice (&agr; phase). After annealing a compression of the lattice has been observed by x‐ray diffraction. The annealing has produced well‐oriented alloys with fairly large domain sizes.