Amorphous ribbons of AlxDy100−x, 93≳x≳85, were obtained by melt spinning. During crystallization, in addition to Al, four different metastable crystalline phases of DyAl3 were observed. These phases are, in order of appearance, the high‐pressure face‐centered cubic phase, γ‐DyAl3 and three polytypic rhombohedral phases, β‐DyAl3, β′‐DyAl3, and α′‐DyAl3. It is the first time that the β′ phase in rare‐earth trialuminides and the α′ phase in Dy‐Al alloy system have been observed. It is shown that all these phases are associated with the polytypic packing of the hexagonal DyAl3 atomic layers. The relative stability of the phases is found to be related to the hexagonal to cubic stacking ratio in the structure.