X-Ray diffraction (XRD) was performed in order to detect p-type Cu-S compounds such as Cu2S in p-type Cu-doped CdS (CdS:Cu) films fabricated by the vacuum deposition of CdS on thin Cu films on a glass substrate. The diffraction angles of CdS:Cu films and the powder corresponded to those of hexagonal US, and their relative peak intensities were also similar to those of the CdS. Lattice constants of the CdS:Cu corresponded to those of hexagonal US within 0.06% of difference. However. some XRD lines of CdS:Cu were close to a few lines of each Cu-S compound. Detailed examination of d-spacings and the relative peak intensities of the diffraction patterns of the CdS:Cu and each Cu-S compound was carried out. However, XRD traces of Cu-S compounds could not be detected in the CdS:Cu films. Therefore. it is thought that crystalline Cu-S compounds were not formed in p-type Cu-doped US films.