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The phase evolution during annealing of Al/Ni multilayer samples prepared by ion‐beam sputtering with composition modulation wavelengths Λ between 10 and 400 nm was determined using x‐ray diffraction and differential scanning calorimeter measurements. Samples with average compositions of Al_0.40Ni_0.60 and Al_0.75Ni_0.25 were investigated. For the Al_0.40Ni_0.60 samples the following results were obtained. A measure of the degree of periodicity and the sharpness of the interfaces in a sample with Λ=80 nm was the large number (over 20) of peaks observed in small‐angle x‐ray scattering measurements. A sample with Λ=10 nm was transformed by heat treatment directly to the AlNi phase. In the Λ=80 nm sample, the first phase formed after annealing was the metastable η phase. The η phase was identified as Al₉Ni₂. In the 400 nm wavelength sample, both the metastable η phase and the stable Al₃Ni …