The structure of samarium disulfide SmS1.9, space group P42/n; lattice constants a = 19.717(2)Å ; c = 15.928(1) Å has been determined and refined by LS method to R = 0.0345; Rw = 0.0419. The structure is a tenfold superstructure from the structure type ZrSSi. [S2]2– dumbbells with interatomic distances 2.146(1)Å between S atoms were observed in the structure. Fully ordered vacancies and orientation of the [S2]2- dumbbells are responsible for the formation of the superstructure. The investigated sample was twinned by the reticular merohedral law, the twin symmetry is 4/mm´m´, the twinning symmetry elements are (310) and (120) mirror planes and the twin index is n=5.