Abstract: Polarized neutron reflectometry is used to study Dy/Gd superlattices with different ratios of Dy- and Gd-layer thicknesses: 1 : 1, 2 : 1, and 3 : 1. It is experimentally shown that the formation of helicoidal magnetic ordering in Dy layers with a period incommensurate with that of the superlattice manifests itself in the appearance of a magnetic-superlattice reflection, which is forbidden due to equality of the thicknesses of alternating Dy and Gd layers with a ratio of 1 : 1. Otherwise, the formation of helicoidal magnetic ordering has little effect on the shape of the neutron-reflectometry curves. Thus, optimization of the structure of rare-earth superlattices for the neutron-reflectometry experiment makes it possible to detect helicoidal magnetic ordering in superlattices with a period incommensurate with the structural superlattice ordering. © 2023, Pleiades Publishing, Ltd.