RE2O2S oxysulfides (with RE = Sm, Eu and Gd) were prepared and characterized regarding their structural and magnetic properties. The compounds crystallized in the trigonal symmetry (space group P-3m/D(3)(3)d), with the lattice parameter varying linearly with the ionic radius of the RE cation. All these oxysulfides are magnetically frustrated and only the gadolinium sample showed magnetic order down to 3 K. The magnetic frustration is attributed to the spatial distribution of cations over the lattice, where the RE's magnetic moments occupy the sites forming a triangular plane lattice, perpendicular to the direction. This geometric magnetic frustration was firstly recognized for these oxysulfides. (C) 2014 Elsevier Ltd. All rights reserved.