Quenched single crystals synthesized at about 550°C in the compositional region about Cu9BiS6 were found to reveal non-integral type satellite reflections. These superstructure peaks have been studied in detail. The substructure obtained using only main reflections is cubic, space group Fm3m, with a = 5.563(1)Å and it has a structure similar to cubic α-chalcocite. Through analysis of the partial Patterson function, the superstructure of the material was found to consist of periodically spaced clusters of Bi and Cu, which are alternately distributed according to a face-centered cubic arrangement. The superstructure shows good agreement between observed and calculated intensities. The repeat distance and the regularity of the long-range ordering appear to change with crystal composition; these observations can be explained on the basis of the structure obtained in this study. The same kind of modulated structure is observed in another quenched material Cu3Bi5S9, in the Cu2S-Bi2S3 system. At high temperature, these phases exist with a disordered metal distribution, and the metal clusters of both materials are considered to be produced during quenching from high temperature.